# This file is a part of Julia. License is MIT: https://julialang.org/license
"""
Methods for working with Iterators.
"""
baremodule Iterators
# small dance to make this work from Base or Intrinsics
import ..@__MODULE__, ..parentmodule
const Base = parentmodule(@__MODULE__)
using .Base:
@inline, Pair, Pairs, AbstractDict, IndexLinear, IndexStyle, AbstractVector, Vector,
SizeUnknown, HasLength, HasShape, IsInfinite, EltypeUnknown, HasEltype, OneTo,
@propagate_inbounds, @isdefined, @boundscheck, @inbounds, Generator,
AbstractRange, AbstractUnitRange, UnitRange, LinearIndices,
(:), |, +, -, *, !==, !, ==, !=, <=, <, >, >=, missing,
any, _counttuple, eachindex, ntuple, zero, prod, reduce, in, firstindex, lastindex,
tail, fieldtypes, min, max, minimum, zero, oneunit, promote, promote_shape
using Core: @doc
if Base !== Core.Compiler
using .Base:
cld, fld, SubArray, view, resize!, IndexCartesian
using .Base.Checked: checked_mul
else
# Checked.checked_mul is not available during bootstrapping:
const checked_mul = *
end
import .Base:
first, last,
isempty, length, size, axes, ndims,
eltype, IteratorSize, IteratorEltype,
haskey, keys, values, pairs,
getindex, setindex!, get, iterate,
popfirst!, isdone, peek, intersect
export enumerate, zip, rest, countfrom, take, drop, takewhile, dropwhile, cycle, repeated, product, flatten, flatmap
if Base !== Core.Compiler
export partition
end
"""
Iterators.map(f, iterators...)
Create a lazy mapping. This is another syntax for writing
`(f(args...) for args in zip(iterators...))`.
!!! compat "Julia 1.6"
This function requires at least Julia 1.6.
# Examples
```jldoctest
julia> collect(Iterators.map(x -> x^2, 1:3))
3-element Vector{Int64}:
1
4
9
```
"""
map(f, args...) = Base.Generator(f, args...)
tail_if_any(::Tuple{}) = ()
tail_if_any(x::Tuple) = tail(x)
_min_length(a, b, ::IsInfinite, ::IsInfinite) = min(length(a),length(b)) # inherit behaviour, error
_min_length(a, b, A, ::IsInfinite) = length(a)
_min_length(a, b, ::IsInfinite, B) = length(b)
_min_length(a, b, A, B) = min(length(a),length(b))
_diff_length(a, b, A, ::IsInfinite) = 0
_diff_length(a, b, ::IsInfinite, ::IsInfinite) = 0
_diff_length(a, b, ::IsInfinite, B) = length(a) # inherit behaviour, error
function _diff_length(a, b, A, B)
m, n = length(a), length(b)
return m > n ? m - n : zero(n - m)
end
and_iteratorsize(isz::T, ::T) where {T} = isz
and_iteratorsize(::HasLength, ::HasShape) = HasLength()
and_iteratorsize(::HasShape, ::HasLength) = HasLength()
and_iteratorsize(a, b) = SizeUnknown()
and_iteratoreltype(iel::T, ::T) where {T} = iel
and_iteratoreltype(a, b) = EltypeUnknown()
## Reverse-order iteration for arrays and other collections. Collections
## should implement iterate etcetera if possible/practical.
"""
Iterators.reverse(itr)
Given an iterator `itr`, then `reverse(itr)` is an iterator over the
same collection but in the reverse order.
This iterator is "lazy" in that it does not make a copy of the collection in
order to reverse it; see [`Base.reverse`](@ref) for an eager implementation.
(By default, this returns
an `Iterators.Reverse` object wrapping `itr`, which is iterable
if the corresponding [`iterate`](@ref) methods are defined, but some `itr` types
may implement more specialized `Iterators.reverse` behaviors.)
Not all iterator types `T` support reverse-order iteration. If `T`
doesn't, then iterating over `Iterators.reverse(itr::T)` will throw a [`MethodError`](@ref)
because of the missing `iterate` methods for `Iterators.Reverse{T}`.
(To implement these methods, the original iterator
`itr::T` can be obtained from an `r::Iterators.Reverse{T}` object by `r.itr`;
more generally, one can use `Iterators.reverse(r)`.)
# Examples
```jldoctest
julia> foreach(println, Iterators.reverse(1:5))
5
4
3
2
1
```
"""
reverse(itr) = Reverse(itr)
struct Reverse{T}
itr::T
end
eltype(::Type{Reverse{T}}) where {T} = eltype(T)
length(r::Reverse) = length(r.itr)
size(r::Reverse) = size(r.itr)
IteratorSize(::Type{Reverse{T}}) where {T} = IteratorSize(T)
IteratorEltype(::Type{Reverse{T}}) where {T} = IteratorEltype(T)
last(r::Reverse) = first(r.itr) # the first shall be last
# reverse-order array iterators: assumes more-specialized Reverse for eachindex
@propagate_inbounds function iterate(A::Reverse{<:AbstractArray}, state=(reverse(eachindex(A.itr)),))
y = iterate(state...)
y === nothing && return y
idx, itrs = y
(A.itr[idx], (state[1], itrs))
end
# Fallback method of `iterate(::Reverse{T})` which assumes the collection has `getindex(::T) and `reverse(eachindex(::T))`
# don't propagate inbounds for this just in case
function iterate(A::Reverse, state=(reverse(eachindex(A.itr)),))
y = iterate(state...)
y === nothing && return y
idx, itrs = y
(A.itr[idx], (state[1], itrs))
end
reverse(R::AbstractRange) = Base.reverse(R) # copying ranges is cheap
reverse(G::Generator) = Generator(G.f, reverse(G.iter))
reverse(r::Reverse) = r.itr
reverse(x::Union{Number,AbstractChar}) = x
reverse(p::Pair) = Base.reverse(p) # copying pairs is cheap
iterate(r::Reverse{<:Union{Tuple, NamedTuple}}, i::Int = length(r.itr)) = i < 1 ? nothing : (r.itr[i], i-1)
# enumerate
struct Enumerate{I}
itr::I
end
"""
enumerate(iter)
An iterator that yields `(i, x)` where `i` is a counter starting at 1,
and `x` is the `i`th value from the given iterator. It's useful when
you need not only the values `x` over which you are iterating, but
also the number of iterations so far.
Note that `i` may not be valid for indexing `iter`, or may index a
different element. This will happen if `iter` has indices that do not
start at 1, and may happen for strings, dictionaries, etc.
See the `pairs(IndexLinear(), iter)` method if you want to ensure that `i` is an index.
# Examples
```jldoctest
julia> a = ["a", "b", "c"];
julia> for (index, value) in enumerate(a)
println("\$index \$value")
end
1 a
2 b
3 c
julia> str = "naïve";
julia> for (i, val) in enumerate(str)
print("i = ", i, ", val = ", val, ", ")
try @show(str[i]) catch e println(e) end
end
i = 1, val = n, str[i] = 'n'
i = 2, val = a, str[i] = 'a'
i = 3, val = ï, str[i] = 'ï'
i = 4, val = v, StringIndexError("naïve", 4)
i = 5, val = e, str[i] = 'v'
```
"""
enumerate(iter) = Enumerate(iter)
length(e::Enumerate) = length(e.itr)
size(e::Enumerate) = size(e.itr)
@propagate_inbounds function iterate(e::Enumerate, state=(1,))
i, rest = state[1], tail(state)
n = iterate(e.itr, rest...)
n === nothing && return n
(i, n[1]), (i+1, n[2])
end
last(e::Enumerate) = (length(e.itr), e.itr[end])
eltype(::Type{Enumerate{I}}) where {I} = Tuple{Int, eltype(I)}
IteratorSize(::Type{Enumerate{I}}) where {I} = IteratorSize(I)
IteratorEltype(::Type{Enumerate{I}}) where {I} = IteratorEltype(I)
@inline function iterate(r::Reverse{<:Enumerate})
ri = reverse(r.itr.itr)
iterate(r, (length(ri), ri))
end
@inline function iterate(r::Reverse{<:Enumerate}, state)
i, ri, rest = state[1], state[2], tail(tail(state))
n = iterate(ri, rest...)
n === nothing && return n
(i, n[1]), (i-1, ri, n[2])
end
"""
pairs(IndexLinear(), A)
pairs(IndexCartesian(), A)
pairs(IndexStyle(A), A)
An iterator that accesses each element of the array `A`, returning
`i => x`, where `i` is the index for the element and `x = A[i]`.
Identical to `pairs(A)`, except that the style of index can be selected.
Also similar to `enumerate(A)`, except `i` will be a valid index
for `A`, while `enumerate` always counts from 1 regardless of the indices
of `A`.
Specifying [`IndexLinear()`](@ref) ensures that `i` will be an integer;
specifying [`IndexCartesian()`](@ref) ensures that `i` will be a
[`Base.CartesianIndex`](@ref); specifying `IndexStyle(A)` chooses whichever has
been defined as the native indexing style for array `A`.
Mutation of the bounds of the underlying array will invalidate this iterator.
# Examples
```jldoctest
julia> A = ["a" "d"; "b" "e"; "c" "f"];
julia> for (index, value) in pairs(IndexStyle(A), A)
println("\$index \$value")
end
1 a
2 b
3 c
4 d
5 e
6 f
julia> S = view(A, 1:2, :);
julia> for (index, value) in pairs(IndexStyle(S), S)
println("\$index \$value")
end
CartesianIndex(1, 1) a
CartesianIndex(2, 1) b
CartesianIndex(1, 2) d
CartesianIndex(2, 2) e
```
See also [`IndexStyle`](@ref), [`axes`](@ref).
"""
pairs(::IndexLinear, A::AbstractArray) = Pairs(A, LinearIndices(A))
# preserve indexing capabilities for known indexable types
# faster than zip(keys(a), values(a)) for arrays
pairs(tuple::Tuple) = Pairs{Int}(tuple, keys(tuple))
pairs(nt::NamedTuple) = Pairs{Symbol}(nt, keys(nt))
pairs(v::Core.SimpleVector) = Pairs(v, LinearIndices(v))
pairs(A::AbstractVector) = pairs(IndexLinear(), A)
# pairs(v::Pairs) = v # listed for reference, but already defined from being an AbstractDict
if Base !== Core.Compiler
pairs(::IndexCartesian, A::AbstractArray) = Pairs(A, Base.CartesianIndices(axes(A)))
pairs(A::AbstractArray) = pairs(IndexCartesian(), A)
end
length(v::Pairs) = length(getfield(v, :itr))
axes(v::Pairs) = axes(getfield(v, :itr))
size(v::Pairs) = size(getfield(v, :itr))
@propagate_inbounds function _pairs_elt(p::Pairs{K, V}, idx) where {K, V}
return Pair{K, V}(idx, getfield(p, :data)[idx])
end
@propagate_inbounds function iterate(p::Pairs{K, V}, state...) where {K, V}
x = iterate(getfield(p, :itr), state...)
x === nothing && return x
idx, next = x
return (_pairs_elt(p, idx), next)
end
@propagate_inbounds function iterate(r::Reverse{<:Pairs}, state=(reverse(getfield(r.itr, :itr)),))
x = iterate(state...)
x === nothing && return x
idx, next = x
return (_pairs_elt(r.itr, idx), (state[1], next))
end
@inline isdone(v::Pairs, state...) = isdone(getfield(v, :itr), state...)
IteratorSize(::Type{<:Pairs{<:Any, <:Any, I}}) where {I} = IteratorSize(I)
IteratorSize(::Type{<:Pairs{<:Any, <:Any, <:AbstractUnitRange, <:Tuple}}) = HasLength()
function last(v::Pairs{K, V}) where {K, V}
idx = last(getfield(v, :itr))
return Pair{K, V}(idx, v[idx])
end
haskey(v::Pairs, key) = (key in getfield(v, :itr))
keys(v::Pairs) = getfield(v, :itr)
values(v::Pairs) = getfield(v, :data) # TODO: this should be a view of data subset by itr
getindex(v::Pairs, key) = getfield(v, :data)[key]
setindex!(v::Pairs, value, key) = (getfield(v, :data)[key] = value; v)
get(v::Pairs, key, default) = get(getfield(v, :data), key, default)
get(f::Base.Callable, v::Pairs, key) = get(f, getfield(v, :data), key)
# zip
struct Zip{Is<:Tuple}
is::Is
end
"""
zip(iters...)
Run multiple iterators at the same time, until any of them is exhausted. The value type of
the `zip` iterator is a tuple of values of its subiterators.
!!! note
`zip` orders the calls to its subiterators in such a way that stateful iterators will
not advance when another iterator finishes in the current iteration.
!!! note
`zip()` with no arguments yields an infinite iterator of empty tuples.
See also: [`enumerate`](@ref), [`Splat`](@ref Base.Splat).
# Examples
```jldoctest
julia> a = 1:5
1:5
julia> b = ["e","d","b","c","a"]
5-element Vector{String}:
"e"
"d"
"b"
"c"
"a"
julia> c = zip(a,b)
zip(1:5, ["e", "d", "b", "c", "a"])
julia> length(c)
5
julia> first(c)
(1, "e")
```
"""
zip(a...) = Zip(a)
function length(z::Zip)
n = _zip_min_length(z.is)
n === nothing && throw(ArgumentError("iterator is of undefined length"))
return n
end
function _zip_min_length(is)
i = is[1]
n = _zip_min_length(tail(is))
if IteratorSize(i) isa IsInfinite
return n
else
return n === nothing ? length(i) : min(n, length(i))
end
end
_zip_min_length(is::Tuple{}) = nothing
size(z::Zip) = _promote_tuple_shape(Base.map(size, z.is)...)
axes(z::Zip) = _promote_tuple_shape(Base.map(axes, z.is)...)
_promote_tuple_shape((a,)::Tuple{OneTo}, (b,)::Tuple{OneTo}) = (intersect(a, b),)
_promote_tuple_shape((m,)::Tuple{Integer}, (n,)::Tuple{Integer}) = (min(m, n),)
_promote_tuple_shape(a, b) = promote_shape(a, b)
_promote_tuple_shape(a, b...) = _promote_tuple_shape(a, _promote_tuple_shape(b...))
_promote_tuple_shape(a) = a
eltype(::Type{Zip{Is}}) where {Is<:Tuple} = Tuple{map(eltype, fieldtypes(Is))...}
#eltype(::Type{Zip{Tuple{}}}) = Tuple{}
#eltype(::Type{Zip{Tuple{A}}}) where {A} = Tuple{eltype(A)}
#eltype(::Type{Zip{Tuple{A, B}}}) where {A, B} = Tuple{eltype(A), eltype(B)}
@inline isdone(z::Zip) = _zip_any_isdone(z.is, Base.map(_ -> (), z.is))
@inline isdone(z::Zip, ss) = _zip_any_isdone(z.is, Base.map(tuple, ss))
@inline function _zip_any_isdone(is, ss)
d1 = isdone(is[1], ss[1]...)
d1 === true && return true
return d1 | _zip_any_isdone(tail(is), tail(ss))
end
@inline _zip_any_isdone(::Tuple{}, ::Tuple{}) = false
@propagate_inbounds iterate(z::Zip) = _zip_iterate_all(z.is, Base.map(_ -> (), z.is))
@propagate_inbounds iterate(z::Zip, ss) = _zip_iterate_all(z.is, Base.map(tuple, ss))
# This first queries isdone from every iterator. If any gives true, it immediately returns
# nothing. It then iterates all those where isdone returned missing, afterwards all those
# it returned false, again terminating immediately if any iterator is exhausted. Finally,
# the results are interleaved appropriately.
@propagate_inbounds function _zip_iterate_all(is, ss)
d, ds = _zip_isdone(is, ss)
d && return nothing
xs1 = _zip_iterate_some(is, ss, ds, missing)
xs1 === nothing && return nothing
xs2 = _zip_iterate_some(is, ss, ds, false)
xs2 === nothing && return nothing
return _zip_iterate_interleave(xs1, xs2, ds)
end
@propagate_inbounds function _zip_iterate_some(is, ss, ds::Tuple{T,Vararg{Any}}, f::T) where T
x = iterate(is[1], ss[1]...)
x === nothing && return nothing
y = _zip_iterate_some(tail(is), tail(ss), tail(ds), f)
y === nothing && return nothing
return (x, y...)
end
@propagate_inbounds _zip_iterate_some(is, ss, ds::Tuple{Any,Vararg{Any}}, f) =
_zip_iterate_some(tail(is), tail(ss), tail(ds), f)
_zip_iterate_some(::Tuple{}, ::Tuple{}, ::Tuple{}, ::Any) = ()
function _zip_iterate_interleave(xs1, xs2, ds)
t = _zip_iterate_interleave(tail(xs1), xs2, tail(ds))
((xs1[1][1], t[1]...), (xs1[1][2], t[2]...))
end
function _zip_iterate_interleave(xs1, xs2, ds::Tuple{Bool,Vararg{Any}})
t = _zip_iterate_interleave(xs1, tail(xs2), tail(ds))
((xs2[1][1], t[1]...), (xs2[1][2], t[2]...))
end
_zip_iterate_interleave(::Tuple{}, ::Tuple{}, ::Tuple{}) = ((), ())
function _zip_isdone(is, ss)
d = isdone(is[1], ss[1]...)
d´, ds = _zip_isdone(tail(is), tail(ss))
return (d === true || d´, (d, ds...))
end
_zip_isdone(::Tuple{}, ::Tuple{}) = (false, ())
IteratorSize(::Type{Zip{Is}}) where {Is<:Tuple} = zip_iteratorsize(ntuple(n -> IteratorSize(fieldtype(Is, n)), _counttuple(Is)::Int)...)
IteratorEltype(::Type{Zip{Is}}) where {Is<:Tuple} = zip_iteratoreltype(ntuple(n -> IteratorEltype(fieldtype(Is, n)), _counttuple(Is)::Int)...)
zip_iteratorsize() = IsInfinite()
zip_iteratorsize(I) = I
zip_iteratorsize(a, b) = and_iteratorsize(a,b) # as `and_iteratorsize` but inherit `Union{HasLength,IsInfinite}` of the shorter iterator
zip_iteratorsize(::HasLength, ::IsInfinite) = HasLength()
zip_iteratorsize(::HasShape, ::IsInfinite) = HasLength()
zip_iteratorsize(a::IsInfinite, b) = zip_iteratorsize(b,a)
zip_iteratorsize(a::IsInfinite, b::IsInfinite) = IsInfinite()
zip_iteratorsize(a, b, tail...) = zip_iteratorsize(a, zip_iteratorsize(b, tail...))
zip_iteratoreltype() = HasEltype()
zip_iteratoreltype(a) = a
zip_iteratoreltype(a, tail...) = and_iteratoreltype(a, zip_iteratoreltype(tail...))
reverse(z::Zip) = Zip(Base.map(reverse, z.is)) # n.b. we assume all iterators are the same length
last(z::Zip) = getindex.(z.is, minimum(Base.map(lastindex, z.is)))
# filter
struct Filter{F,I}
flt::F
itr::I
end
"""
Iterators.filter(flt, itr)
Given a predicate function `flt` and an iterable object `itr`, return an
iterable object which upon iteration yields the elements `x` of `itr` that
satisfy `flt(x)`. The order of the original iterator is preserved.
This function is *lazy*; that is, it is guaranteed to return in ``Θ(1)`` time
and use ``Θ(1)`` additional space, and `flt` will not be called by an
invocation of `filter`. Calls to `flt` will be made when iterating over the
returned iterable object. These calls are not cached and repeated calls will be
made when reiterating.
See [`Base.filter`](@ref) for an eager implementation of filtering for arrays.
# Examples
```jldoctest
julia> f = Iterators.filter(isodd, [1, 2, 3, 4, 5])
Base.Iterators.Filter{typeof(isodd), Vector{Int64}}(isodd, [1, 2, 3, 4, 5])
julia> foreach(println, f)
1
3
5
julia> [x for x in [1, 2, 3, 4, 5] if isodd(x)] # collects a generator over Iterators.filter
3-element Vector{Int64}:
1
3
5
```
"""
filter(flt, itr) = Filter(flt, itr)
function iterate(f::Filter, state...)
y = iterate(f.itr, state...)
while y !== nothing
if f.flt(y[1])
return y
end
y = iterate(f.itr, y[2])
end
nothing
end
eltype(::Type{Filter{F,I}}) where {F,I} = eltype(I)
IteratorEltype(::Type{Filter{F,I}}) where {F,I} = IteratorEltype(I)
IteratorSize(::Type{<:Filter}) = SizeUnknown()
reverse(f::Filter) = Filter(f.flt, reverse(f.itr))
last(f::Filter) = first(reverse(f))
# Accumulate -- partial reductions of a function over an iterator
struct Accumulate{F,I,T}
f::F
itr::I
init::T
end
"""
Iterators.accumulate(f, itr; [init])
Given a 2-argument function `f` and an iterator `itr`, return a new
iterator that successively applies `f` to the previous value and the
next element of `itr`.
This is effectively a lazy version of [`Base.accumulate`](@ref).
!!! compat "Julia 1.5"
Keyword argument `init` is added in Julia 1.5.
# Examples
```jldoctest
julia> a = Iterators.accumulate(+, [1,2,3,4]);
julia> foreach(println, a)
1
3
6
10
julia> b = Iterators.accumulate(/, (2, 5, 2, 5); init = 100);
julia> collect(b)
4-element Vector{Float64}:
50.0
10.0
5.0
1.0
```
"""
accumulate(f, itr; init = Base._InitialValue()) = Accumulate(f, itr, init)
function iterate(itr::Accumulate)
state = iterate(itr.itr)
if state === nothing
return nothing
end
val = Base.BottomRF(itr.f)(itr.init, state[1])
return (val, (val, state[2]))
end
function iterate(itr::Accumulate, state)
nxt = iterate(itr.itr, state[2])
if nxt === nothing
return nothing
end
val = itr.f(state[1], nxt[1])
return (val, (val, nxt[2]))
end
length(itr::Accumulate) = length(itr.itr)
size(itr::Accumulate) = size(itr.itr)
IteratorSize(::Type{<:Accumulate{<:Any,I}}) where {I} = IteratorSize(I)
IteratorEltype(::Type{<:Accumulate}) = EltypeUnknown()
# Rest -- iterate starting at the given state
struct Rest{I,S}
itr::I
st::S
end
"""
rest(iter, state)
An iterator that yields the same elements as `iter`, but starting at the given `state`.
See also: [`Iterators.drop`](@ref), [`Iterators.peel`](@ref), [`Base.rest`](@ref).
# Examples
```jldoctest
julia> collect(Iterators.rest([1,2,3,4], 2))
3-element Vector{Int64}:
2
3
4
```
"""
rest(itr,state) = Rest(itr,state)
rest(itr::Rest,state) = Rest(itr.itr,state)
rest(itr) = itr
"""
peel(iter)
Returns the first element and an iterator over the remaining elements.
If the iterator is empty return `nothing` (like `iterate`).
!!! compat "Julia 1.7"
Prior versions throw a BoundsError if the iterator is empty.
See also: [`Iterators.drop`](@ref), [`Iterators.take`](@ref).
# Examples
```jldoctest
julia> (a, rest) = Iterators.peel("abc");
julia> a
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> collect(rest)
2-element Vector{Char}:
'b': ASCII/Unicode U+0062 (category Ll: Letter, lowercase)
'c': ASCII/Unicode U+0063 (category Ll: Letter, lowercase)
```
"""
function peel(itr)
y = iterate(itr)
y === nothing && return y
val, s = y
val, rest(itr, s)
end
@propagate_inbounds iterate(i::Rest, st=i.st) = iterate(i.itr, st)
isdone(i::Rest, st...) = isdone(i.itr, st...)
eltype(::Type{<:Rest{I}}) where {I} = eltype(I)
IteratorEltype(::Type{<:Rest{I}}) where {I} = IteratorEltype(I)
rest_iteratorsize(a) = SizeUnknown()
rest_iteratorsize(::IsInfinite) = IsInfinite()
IteratorSize(::Type{<:Rest{I}}) where {I} = rest_iteratorsize(IteratorSize(I))
# Count -- infinite counting
struct Count{T,S}
start::T
step::S
end
"""
countfrom(start=1, step=1)
An iterator that counts forever, starting at `start` and incrementing by `step`.
# Examples
```jldoctest
julia> for v in Iterators.countfrom(5, 2)
v > 10 && break
println(v)
end
5
7
9
```
"""
countfrom(start::T, step::S) where {T,S} = Count{typeof(start+step),S}(start, step)
countfrom(start::Number, step::Number) = Count(promote(start, step)...)
countfrom(start) = Count(start, oneunit(start))
countfrom() = Count(1, 1)
eltype(::Type{<:Count{T}}) where {T} = T
iterate(it::Count, state=it.start) = (state, state + it.step)
IteratorSize(::Type{<:Count}) = IsInfinite()
# Take -- iterate through the first n elements
struct Take{I}
xs::I
n::Int
function Take(xs::I, n::Integer) where {I}
n < 0 && throw(ArgumentError("Take length must be nonnegative"))
return new{I}(xs, n)
end
end
"""
take(iter, n)
An iterator that generates at most the first `n` elements of `iter`.
See also: [`drop`](@ref Iterators.drop), [`peel`](@ref Iterators.peel), [`first`](@ref), [`Base.take!`](@ref).
# Examples
```jldoctest
julia> a = 1:2:11
1:2:11
julia> collect(a)
6-element Vector{Int64}:
1
3
5
7
9
11
julia> collect(Iterators.take(a,3))
3-element Vector{Int64}:
1
3
5
```
"""
take(xs, n::Integer) = Take(xs, Int(n))
take(xs::Take, n::Integer) = Take(xs.xs, min(Int(n), xs.n))
eltype(::Type{Take{I}}) where {I} = eltype(I)
IteratorEltype(::Type{Take{I}}) where {I} = IteratorEltype(I)
take_iteratorsize(a) = HasLength()
take_iteratorsize(::SizeUnknown) = SizeUnknown()
IteratorSize(::Type{Take{I}}) where {I} = take_iteratorsize(IteratorSize(I))
length(t::Take) = _min_length(t.xs, 1:t.n, IteratorSize(t.xs), HasLength())
isdone(t::Take) = isdone(t.xs)
isdone(t::Take, state) = (state[1] <= 0) | isdone(t.xs, tail(state))
@propagate_inbounds function iterate(it::Take, state=(it.n,))
n, rest = state[1], tail(state)
n <= 0 && return nothing
y = iterate(it.xs, rest...)
y === nothing && return nothing
return y[1], (n - 1, y[2])
end
# Drop -- iterator through all but the first n elements
struct Drop{I}
xs::I
n::Int
function Drop(xs::I, n::Integer) where {I}
n < 0 && throw(ArgumentError("Drop length must be nonnegative"))
return new{I}(xs, n)
end
end
"""
drop(iter, n)
An iterator that generates all but the first `n` elements of `iter`.
# Examples
```jldoctest
julia> a = 1:2:11
1:2:11
julia> collect(a)
6-element Vector{Int64}:
1
3
5
7
9
11
julia> collect(Iterators.drop(a,4))
2-element Vector{Int64}:
9
11
```
"""
drop(xs, n::Integer) = Drop(xs, Int(n))
drop(xs::Take, n::Integer) = Take(drop(xs.xs, Int(n)), max(0, xs.n - Int(n)))
drop(xs::Drop, n::Integer) = Drop(xs.xs, Int(n) + xs.n)
eltype(::Type{Drop{I}}) where {I} = eltype(I)
IteratorEltype(::Type{Drop{I}}) where {I} = IteratorEltype(I)
drop_iteratorsize(::SizeUnknown) = SizeUnknown()
drop_iteratorsize(::Union{HasShape, HasLength}) = HasLength()
drop_iteratorsize(::IsInfinite) = IsInfinite()
IteratorSize(::Type{Drop{I}}) where {I} = drop_iteratorsize(IteratorSize(I))
length(d::Drop) = _diff_length(d.xs, 1:d.n, IteratorSize(d.xs), HasLength())
function iterate(it::Drop)
y = iterate(it.xs)
for i in 1:it.n
y === nothing && return y
y = iterate(it.xs, y[2])
end
y
end
iterate(it::Drop, state) = iterate(it.xs, state)
isdone(it::Drop, state) = isdone(it.xs, state)
# takewhile
struct TakeWhile{I,P<:Function}
pred::P
xs::I
end
"""
takewhile(pred, iter)
An iterator that generates element from `iter` as long as predicate `pred` is true,
afterwards, drops every element.
!!! compat "Julia 1.4"
This function requires at least Julia 1.4.
# Examples
```jldoctest
julia> s = collect(1:5)
5-element Vector{Int64}:
1
2
3
4
5
julia> collect(Iterators.takewhile(<(3),s))
2-element Vector{Int64}:
1
2
```
"""
takewhile(pred,xs) = TakeWhile(pred,xs)
function iterate(ibl::TakeWhile, itr...)
y = iterate(ibl.xs,itr...)
y === nothing && return nothing
ibl.pred(y[1]) || return nothing
y
end
IteratorSize(::Type{<:TakeWhile}) = SizeUnknown()
eltype(::Type{TakeWhile{I,P}} where P) where {I} = eltype(I)
IteratorEltype(::Type{TakeWhile{I, P}} where P) where {I} = IteratorEltype(I)
# dropwhile
struct DropWhile{I,P<:Function}
pred::P
xs::I
end
"""
dropwhile(pred, iter)
An iterator that drops element from `iter` as long as predicate `pred` is true,
afterwards, returns every element.
!!! compat "Julia 1.4"
This function requires at least Julia 1.4.
# Examples
```jldoctest
julia> s = collect(1:5)
5-element Vector{Int64}:
1
2
3
4
5
julia> collect(Iterators.dropwhile(<(3),s))
3-element Vector{Int64}:
3
4
5
```
"""
dropwhile(pred,itr) = DropWhile(pred,itr)
iterate(ibl::DropWhile,itr) = iterate(ibl.xs, itr)
function iterate(ibl::DropWhile)
y = iterate(ibl.xs)
while y !== nothing
ibl.pred(y[1]) || break
y = iterate(ibl.xs,y[2])
end
y
end
IteratorSize(::Type{<:DropWhile}) = SizeUnknown()
eltype(::Type{DropWhile{I,P}}) where {I,P} = eltype(I)
IteratorEltype(::Type{DropWhile{I,P}}) where {I,P} = IteratorEltype(I)
# Cycle an iterator forever
struct Cycle{I}
xs::I
end
"""
cycle(iter)
An iterator that cycles through `iter` forever.
If `iter` is empty, so is `cycle(iter)`.
See also: [`Iterators.repeated`](@ref), [`Base.repeat`](@ref).
# Examples
```jldoctest
julia> for (i, v) in enumerate(Iterators.cycle("hello"))
print(v)
i > 10 && break
end
hellohelloh
```
"""
cycle(xs) = Cycle(xs)
eltype(::Type{Cycle{I}}) where {I} = eltype(I)
IteratorEltype(::Type{Cycle{I}}) where {I} = IteratorEltype(I)
IteratorSize(::Type{Cycle{I}}) where {I} = IsInfinite()
iterate(it::Cycle) = iterate(it.xs)
isdone(it::Cycle) = isdone(it.xs)
isdone(it::Cycle, state) = false
function iterate(it::Cycle, state)
y = iterate(it.xs, state)
y === nothing && return iterate(it)
y
end
reverse(it::Cycle) = Cycle(reverse(it.xs))
last(it::Cycle) = last(it.xs)
# Repeated - repeat an object infinitely many times
struct Repeated{O}
x::O
end
repeated(x) = Repeated(x)
"""
repeated(x[, n::Int])
An iterator that generates the value `x` forever. If `n` is specified, generates `x` that
many times (equivalent to `take(repeated(x), n)`).
See also: [`Iterators.cycle`](@ref), [`Base.repeat`](@ref).
# Examples
```jldoctest
julia> a = Iterators.repeated([1 2], 4);
julia> collect(a)
4-element Vector{Matrix{Int64}}:
[1 2]
[1 2]
[1 2]
[1 2]
```
"""
repeated(x, n::Integer) = take(repeated(x), Int(n))
eltype(::Type{Repeated{O}}) where {O} = O
iterate(it::Repeated, state...) = (it.x, nothing)
IteratorSize(::Type{<:Repeated}) = IsInfinite()
IteratorEltype(::Type{<:Repeated}) = HasEltype()
reverse(it::Union{Repeated,Take{<:Repeated}}) = it
last(it::Union{Repeated,Take{<:Repeated}}) = first(it)
# Product -- cartesian product of iterators
struct ProductIterator{T<:Tuple}
iterators::T
end
"""
product(iters...)
Return an iterator over the product of several iterators. Each generated element is
a tuple whose `i`th element comes from the `i`th argument iterator. The first iterator
changes the fastest.
See also: [`zip`](@ref), [`Iterators.flatten`](@ref).
# Examples
```jldoctest
julia> collect(Iterators.product(1:2, 3:5))
2×3 Matrix{Tuple{Int64, Int64}}:
(1, 3) (1, 4) (1, 5)
(2, 3) (2, 4) (2, 5)
julia> ans == [(x,y) for x in 1:2, y in 3:5] # collects a generator involving Iterators.product
true
```
"""
product(iters...) = ProductIterator(iters)
IteratorSize(::Type{ProductIterator{Tuple{}}}) = HasShape{0}()
IteratorSize(::Type{ProductIterator{T}}) where {T<:Tuple} =
prod_iteratorsize(ntuple(n -> IteratorSize(fieldtype(T, n)), _counttuple(T)::Int)..., HasShape{0}())
prod_iteratorsize() = HasShape{0}()
prod_iteratorsize(I) = I
prod_iteratorsize(::HasLength, ::HasLength) = HasShape{2}()
prod_iteratorsize(::HasLength, ::HasShape{N}) where {N} = HasShape{N+1}()
prod_iteratorsize(::HasShape{N}, ::HasLength) where {N} = HasShape{N+1}()
prod_iteratorsize(::HasShape{M}, ::HasShape{N}) where {M,N} = HasShape{M+N}()
# products can have an infinite iterator
prod_iteratorsize(::IsInfinite, ::IsInfinite) = IsInfinite()
prod_iteratorsize(a, ::IsInfinite) = IsInfinite()
prod_iteratorsize(::IsInfinite, b) = IsInfinite()
prod_iteratorsize(a, b) = SizeUnknown()
prod_iteratorsize(a, b, tail...) = prod_iteratorsize(a, prod_iteratorsize(b, tail...))
size(P::ProductIterator) = _prod_size(P.iterators)
_prod_size(::Tuple{}) = ()
_prod_size(t::Tuple) = (_prod_size1(t[1], IteratorSize(t[1]))..., _prod_size(tail(t))...)
_prod_size1(a, ::HasShape) = size(a)
_prod_size1(a, ::HasLength) = (length(a),)
_prod_size1(a, A) =
throw(ArgumentError("Cannot compute size for object of type $(typeof(a))"))
axes(P::ProductIterator) = _prod_indices(P.iterators)
_prod_indices(::Tuple{}) = ()
_prod_indices(t::Tuple) = (_prod_axes1(t[1], IteratorSize(t[1]))..., _prod_indices(tail(t))...)
_prod_axes1(a, ::HasShape) = axes(a)
_prod_axes1(a, ::HasLength) = (OneTo(length(a)),)
_prod_axes1(a, A) =
throw(ArgumentError("Cannot compute indices for object of type $(typeof(a))"))
ndims(p::ProductIterator) = length(axes(p))
length(P::ProductIterator) = reduce(checked_mul, size(P); init=1)
IteratorEltype(::Type{ProductIterator{Tuple{}}}) = HasEltype()
IteratorEltype(::Type{ProductIterator{Tuple{I}}}) where {I} = IteratorEltype(I)
function IteratorEltype(::Type{ProductIterator{T}}) where {T<:Tuple}
E = ntuple(n -> IteratorEltype(fieldtype(T, n)), _counttuple(T)::Int)
any(I -> I == EltypeUnknown(), E) && return EltypeUnknown()
return E[end]
end
eltype(::Type{ProductIterator{I}}) where {I} = _prod_eltype(I)
_prod_eltype(::Type{Tuple{}}) = Tuple{}
_prod_eltype(::Type{I}) where {I<:Tuple} =
Tuple{ntuple(n -> eltype(fieldtype(I, n)), _counttuple(I)::Int)...}
iterate(::ProductIterator{Tuple{}}) = (), true
iterate(::ProductIterator{Tuple{}}, state) = nothing
@inline isdone(P::ProductIterator) = any(isdone, P.iterators)
@inline function _pisdone(iters, states)
iter1 = first(iters)
done1 = isdone(iter1, first(states)[2]) # check step
done1 === true || return done1 # false or missing
done1 = isdone(iter1) # check restart
done1 === true || return done1 # false or missing
return _pisdone(tail(iters), tail(states)) # check tail
end
@inline isdone(::ProductIterator{Tuple{}}, states) = true
@inline isdone(P::ProductIterator, states) = _pisdone(P.iterators, states)
@inline _piterate() = ()
@inline function _piterate(iter1, rest...)
next = iterate(iter1)
next === nothing && return nothing
restnext = _piterate(rest...)
restnext === nothing && return nothing
return (next, restnext...)
end
@inline function iterate(P::ProductIterator)
isdone(P) === true && return nothing
next = _piterate(P.iterators...)
next === nothing && return nothing
return (Base.map(x -> x[1], next), next)
end
@inline _piterate1(::Tuple{}, ::Tuple{}) = nothing
@inline function _piterate1(iters, states)
iter1 = first(iters)
next = iterate(iter1, first(states)[2])
restnext = tail(states)
if next === nothing
isdone(iter1) === true && return nothing
restnext = _piterate1(tail(iters), restnext)
restnext === nothing && return nothing
next = iterate(iter1)
next === nothing && return nothing
end
return (next, restnext...)
end
@inline function iterate(P::ProductIterator, states)
isdone(P, states) === true && return nothing
next = _piterate1(P.iterators, states)
next === nothing && return nothing
return (Base.map(x -> x[1], next), next)
end
reverse(p::ProductIterator) = ProductIterator(Base.map(reverse, p.iterators))
last(p::ProductIterator) = Base.map(last, p.iterators)
intersect(a::ProductIterator, b::ProductIterator) = ProductIterator(intersect.(a.iterators, b.iterators))
# flatten an iterator of iterators
struct Flatten{I}
it::I
end
"""
flatten(iter)
Given an iterator that yields iterators, return an iterator that yields the
elements of those iterators.
Put differently, the elements of the argument iterator are concatenated.
# Examples
```jldoctest
julia> collect(Iterators.flatten((1:2, 8:9)))
4-element Vector{Int64}:
1
2
8
9
julia> [(x,y) for x in 0:1 for y in 'a':'c'] # collects generators involving Iterators.flatten
6-element Vector{Tuple{Int64, Char}}:
(0, 'a')
(0, 'b')
(0, 'c')
(1, 'a')
(1, 'b')
(1, 'c')
```
"""
flatten(itr) = Flatten(itr)
eltype(::Type{Flatten{I}}) where {I} = eltype(eltype(I))
eltype(::Type{Flatten{Tuple{}}}) = eltype(Tuple{})
IteratorEltype(::Type{Flatten{I}}) where {I} = _flatteneltype(I, IteratorEltype(I))
IteratorEltype(::Type{Flatten{Tuple{}}}) = IteratorEltype(Tuple{})
_flatteneltype(I, ::HasEltype) = IteratorEltype(eltype(I))
_flatteneltype(I, et) = EltypeUnknown()
flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{<:NTuple{N,Any}}) where {N} = HasLength()
flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{<:Tuple}) = SizeUnknown()
flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{<:Number}) = HasLength()
flatten_iteratorsize(a, b) = SizeUnknown()
_flatten_iteratorsize(sz, ::EltypeUnknown, I) = SizeUnknown()
_flatten_iteratorsize(sz, ::HasEltype, I) = flatten_iteratorsize(sz, eltype(I))
_flatten_iteratorsize(sz, ::HasEltype, ::Type{Tuple{}}) = HasLength()
IteratorSize(::Type{Flatten{I}}) where {I} = _flatten_iteratorsize(IteratorSize(I), IteratorEltype(I), I)
function flatten_length(f, T::Type{<:NTuple{N,Any}}) where {N}
return N * length(f.it)
end
flatten_length(f, ::Type{<:Number}) = length(f.it)
flatten_length(f, T) = throw(ArgumentError(
"Iterates of the argument to Flatten are not known to have constant length"))
length(f::Flatten{I}) where {I} = flatten_length(f, eltype(I))
length(f::Flatten{Tuple{}}) = 0
@propagate_inbounds function iterate(f::Flatten, state=())
if state !== ()
y = iterate(tail(state)...)
y !== nothing && return (y[1], (state[1], state[2], y[2]))
end
x = (state === () ? iterate(f.it) : iterate(f.it, state[1]))
x === nothing && return nothing
y = iterate(x[1])
while y === nothing
x = iterate(f.it, x[2])
x === nothing && return nothing
y = iterate(x[1])
end
return y[1], (x[2], x[1], y[2])
end
reverse(f::Flatten) = Flatten(reverse(itr) for itr in reverse(f.it))
last(f::Flatten) = last(last(f.it))
"""
Iterators.flatmap(f, iterators...)
Equivalent to `flatten(map(f, iterators...))`.
See also [`Iterators.flatten`](@ref), [`Iterators.map`](@ref).
!!! compat "Julia 1.9"
This function was added in Julia 1.9.
# Examples
```jldoctest
julia> Iterators.flatmap(n -> -n:2:n, 1:3) |> collect
9-element Vector{Int64}:
-1
1
-2
0
2
-3
-1
1
3
julia> stack(n -> -n:2:n, 1:3)
ERROR: DimensionMismatch: stack expects uniform slices, got axes(x) == (1:3,) while first had (1:2,)
[...]
julia> Iterators.flatmap(n -> (-n, 10n), 1:2) |> collect
4-element Vector{Int64}:
-1
10
-2
20
julia> ans == vec(stack(n -> (-n, 10n), 1:2))
true
```
"""
flatmap(f, c...) = flatten(map(f, c...))
if Base !== Core.Compiler # views are not defined
@doc """
partition(collection, n)
Iterate over a collection `n` elements at a time.
# Examples
```jldoctest
julia> collect(Iterators.partition([1,2,3,4,5], 2))
3-element Vector{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}}:
[1, 2]
[3, 4]
[5]
```
""" function partition(c, n::Integer)
n < 1 && throw(ArgumentError("cannot create partitions of length $n"))
return PartitionIterator(c, Int(n))
end
struct PartitionIterator{T}
c::T
n::Int
end
# Partitions are explicitly a linear indexing operation, so reshape to 1-d immediately
PartitionIterator(A::AbstractArray, n::Int) = PartitionIterator(Base.vec(A), n)
PartitionIterator(v::AbstractVector, n::Int) = PartitionIterator{typeof(v)}(v, n)
eltype(::Type{PartitionIterator{T}}) where {T} = Vector{eltype(T)}
# Arrays use a generic `view`-of-a-`vec`, so we cannot exactly predict what we'll get back
eltype(::Type{PartitionIterator{T}}) where {T<:AbstractArray} = AbstractVector{eltype(T)}
# But for some common implementations in Base we know the answer exactly
eltype(::Type{PartitionIterator{T}}) where {T<:Vector} = SubArray{eltype(T), 1, T, Tuple{UnitRange{Int}}, true}
IteratorEltype(::Type{PartitionIterator{T}}) where {T} = IteratorEltype(T)
IteratorEltype(::Type{PartitionIterator{T}}) where {T<:AbstractArray} = EltypeUnknown()
IteratorEltype(::Type{PartitionIterator{T}}) where {T<:Vector} = IteratorEltype(T)
partition_iteratorsize(::HasShape) = HasLength()
partition_iteratorsize(isz) = isz
function IteratorSize(::Type{PartitionIterator{T}}) where {T}
partition_iteratorsize(IteratorSize(T))
end
function length(itr::PartitionIterator)
l = length(itr.c)
return cld(l, itr.n)
end
function iterate(itr::PartitionIterator{<:AbstractRange}, state = firstindex(itr.c))
state > lastindex(itr.c) && return nothing
r = min(state + itr.n - 1, lastindex(itr.c))
return @inbounds itr.c[state:r], r + 1
end
function iterate(itr::PartitionIterator{<:AbstractArray}, state = firstindex(itr.c))
state > lastindex(itr.c) && return nothing
r = min(state + itr.n - 1, lastindex(itr.c))
return @inbounds view(itr.c, state:r), r + 1
end
struct IterationCutShort; end
function iterate(itr::PartitionIterator, state...)
# This is necessary to remember whether we cut the
# last element short. In such cases, we do return that
# element, but not the next one
state === (IterationCutShort(),) && return nothing
v = Vector{eltype(itr.c)}(undef, itr.n)
i = 0
y = iterate(itr.c, state...)
while y !== nothing
i += 1
v[i] = y[1]
if i >= itr.n
break
end
y = iterate(itr.c, y[2])
end
i === 0 && return nothing
return resize!(v, i), y === nothing ? IterationCutShort() : y[2]
end
@doc """
Stateful(itr)
There are several different ways to think about this iterator wrapper:
1. It provides a mutable wrapper around an iterator and
its iteration state.
2. It turns an iterator-like abstraction into a `Channel`-like
abstraction.
3. It's an iterator that mutates to become its own rest iterator
whenever an item is produced.
`Stateful` provides the regular iterator interface. Like other mutable iterators
(e.g. [`Base.Channel`](@ref)), if iteration is stopped early (e.g. by a [`break`](@ref) in a [`for`](@ref) loop),
iteration can be resumed from the same spot by continuing to iterate over the
same iterator object (in contrast, an immutable iterator would restart from the
beginning).
# Examples
```jldoctest
julia> a = Iterators.Stateful("abcdef");
julia> isempty(a)
false
julia> popfirst!(a)
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> collect(Iterators.take(a, 3))
3-element Vector{Char}:
'b': ASCII/Unicode U+0062 (category Ll: Letter, lowercase)
'c': ASCII/Unicode U+0063 (category Ll: Letter, lowercase)
'd': ASCII/Unicode U+0064 (category Ll: Letter, lowercase)
julia> collect(a)
2-element Vector{Char}:
'e': ASCII/Unicode U+0065 (category Ll: Letter, lowercase)
'f': ASCII/Unicode U+0066 (category Ll: Letter, lowercase)
julia> Iterators.reset!(a); popfirst!(a)
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> Iterators.reset!(a, "hello"); popfirst!(a)
'h': ASCII/Unicode U+0068 (category Ll: Letter, lowercase)
```
```jldoctest
julia> a = Iterators.Stateful([1,1,1,2,3,4]);
julia> for x in a; x == 1 || break; end
julia> peek(a)
3
julia> sum(a) # Sum the remaining elements
7
```
"""
mutable struct Stateful{T, VS, N<:Integer}
itr::T
# A bit awkward right now, but adapted to the new iteration protocol
nextvalstate::Union{VS, Nothing}
# Number of remaining elements, if itr is HasLength or HasShape.
# if not, store -1 - number_of_consumed_elements.
# This allows us to defer calculating length until asked for.
# See PR #45924
remaining::N
@inline function Stateful{<:Any, Any}(itr::T) where {T}
itl = iterlength(itr)
new{T, Any, typeof(itl)}(itr, iterate(itr), itl)
end
@inline function Stateful(itr::T) where {T}
VS = approx_iter_type(T)
itl = iterlength(itr)
return new{T, VS, typeof(itl)}(itr, iterate(itr)::VS, itl)
end
end
function iterlength(it)::Signed
if IteratorSize(it) isa Union{HasShape, HasLength}
return length(it)
else
-1
end
end
function reset!(s::Stateful{T,VS}, itr::T=s.itr) where {T,VS}
s.itr = itr
itl = iterlength(itr)
setfield!(s, :nextvalstate, iterate(itr))
s.remaining = itl
s
end
# Try to find an appropriate type for the (value, state tuple),
# by doing a recursive unrolling of the iteration protocol up to
# fixpoint.
approx_iter_type(itrT::Type) = _approx_iter_type(itrT, Base._return_type(iterate, Tuple{itrT}))
# Not actually called, just passed to return type to avoid
# having to typesplit on Nothing
function doiterate(itr, valstate::Union{Nothing, Tuple{Any, Any}})
valstate === nothing && return nothing
val, st = valstate
return iterate(itr, st)
end
function _approx_iter_type(itrT::Type, vstate::Type)
vstate <: Union{Nothing, Tuple{Any, Any}} || return Any
vstate <: Union{} && return Union{}
nextvstate = Base._return_type(doiterate, Tuple{itrT, vstate})
return (nextvstate <: vstate ? vstate : Any)
end
Stateful(x::Stateful) = x
convert(::Type{Stateful}, itr) = Stateful(itr)
@inline isdone(s::Stateful, st=nothing) = s.nextvalstate === nothing
@inline function popfirst!(s::Stateful)
vs = s.nextvalstate
if vs === nothing
throw(Base.EOFError())
else
val, state = vs
Core.setfield!(s, :nextvalstate, iterate(s.itr, state))
rem = s.remaining
s.remaining = rem - typeof(rem)(1)
return val
end
end
@inline function peek(s::Stateful, sentinel=nothing)
ns = s.nextvalstate
return ns !== nothing ? ns[1] : sentinel
end
@inline iterate(s::Stateful, state=nothing) = s.nextvalstate === nothing ? nothing : (popfirst!(s), nothing)
IteratorSize(::Type{<:Stateful{T}}) where {T} = IteratorSize(T) isa HasShape ? HasLength() : IteratorSize(T)
eltype(::Type{<:Stateful{T}}) where {T} = eltype(T)
IteratorEltype(::Type{<:Stateful{T}}) where {T} = IteratorEltype(T)
function length(s::Stateful)
rem = s.remaining
# If rem is actually remaining length, return it.
# else, rem is number of consumed elements.
if rem >= 0
rem
else
length(s.itr) - (typeof(rem)(1) - rem)
end
end
end # if statement several hundred lines above
"""
only(x)
Return the one and only element of collection `x`, or throw an [`ArgumentError`](@ref) if the
collection has zero or multiple elements.
See also [`first`](@ref), [`last`](@ref).
!!! compat "Julia 1.4"
This method requires at least Julia 1.4.
# Examples
```jldoctest
julia> only(["a"])
"a"
julia> only("a")
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> only(())
ERROR: ArgumentError: Tuple contains 0 elements, must contain exactly 1 element
Stacktrace:
[...]
julia> only(('a', 'b'))
ERROR: ArgumentError: Tuple contains 2 elements, must contain exactly 1 element
Stacktrace:
[...]
```
"""
@propagate_inbounds function only(x)
i = iterate(x)
@boundscheck if i === nothing
throw(ArgumentError("Collection is empty, must contain exactly 1 element"))
end
(ret, state) = i::NTuple{2,Any}
@boundscheck if iterate(x, state) !== nothing
throw(ArgumentError("Collection has multiple elements, must contain exactly 1 element"))
end
return ret
end
# Collections of known size
only(x::Ref) = x[]
only(x::Number) = x
only(x::Char) = x
only(x::Tuple{Any}) = x[1]
only(x::Tuple) = throw(
ArgumentError("Tuple contains $(length(x)) elements, must contain exactly 1 element")
)
only(a::AbstractArray{<:Any, 0}) = @inbounds return a[]
only(x::NamedTuple{<:Any, <:Tuple{Any}}) = first(x)
only(x::NamedTuple) = throw(
ArgumentError("NamedTuple contains $(length(x)) elements, must contain exactly 1 element")
)
end