Revision fb670345366611421b2e04212289d44f69b75096 authored by Jeff Bezanson on 28 March 2017, 15:15:28 UTC, committed by Jeff Bezanson on 28 March 2017, 15:15:28 UTC
1 parent f7d7665
iterators.jl
# This file is a part of Julia. License is MIT: http://julialang.org/license
module Iterators
import Base: start, done, next, isempty, length, size, eltype, iteratorsize, iteratoreltype, indices, ndims
using Base: tuple_type_cons, SizeUnknown, HasLength, HasShape, IsInfinite, EltypeUnknown, HasEltype, OneTo, @propagate_inbounds
export enumerate, zip, rest, countfrom, take, drop, cycle, repeated, product, flatten, partition
_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
_diff_length(a, b, A, B) = max(length(a)-length(b), 0)
and_iteratorsize{T}(isz::T, ::T) = isz
and_iteratorsize(::HasLength, ::HasShape) = HasLength()
and_iteratorsize(::HasShape, ::HasLength) = HasLength()
and_iteratorsize(a, b) = SizeUnknown()
and_iteratoreltype{T}(iel::T, ::T) = iel
and_iteratoreltype(a, b) = EltypeUnknown()
# 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`; it's also possible that `x != iter[i]`, if `iter`
has indices that do not start at 1. See the `enumerate(IndexLinear(),
iter)` method if you want to ensure that `i` is an index.
```jldoctest
julia> a = ["a", "b", "c"];
julia> for (index, value) in enumerate(a)
println("\$index \$value")
end
1 a
2 b
3 c
```
"""
enumerate(iter) = Enumerate(iter)
length(e::Enumerate) = length(e.itr)
size(e::Enumerate) = size(e.itr)
@inline start(e::Enumerate) = (1, start(e.itr))
@inline function next(e::Enumerate, state)
n = next(e.itr,state[2])
(state[1],n[1]), (state[1]+1,n[2])
end
@inline done(e::Enumerate, state) = done(e.itr, state[2])
eltype{I}(::Type{Enumerate{I}}) = Tuple{Int, eltype(I)}
iteratorsize{I}(::Type{Enumerate{I}}) = iteratorsize(I)
iteratoreltype{I}(::Type{Enumerate{I}}) = iteratoreltype(I)
struct IndexValue{I,A<:AbstractArray}
data::A
itr::I
end
"""
enumerate(IndexLinear(), A)
enumerate(IndexCartesian(), A)
enumerate(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]`. This
is similar to `enumerate(A)`, except `i` will always be a valid index
for `A`.
Specifying `IndexLinear()` ensures that `i` will be an integer;
specifying `IndexCartesian()` ensures that `i` will be a
`CartesianIndex`; specifying `IndexStyle(A)` chooses whichever has
been defined as the native indexing style for array `A`.
```jldoctest
julia> A = ["a" "d"; "b" "e"; "c" "f"];
julia> for (index, value) in enumerate(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 enumerate(IndexStyle(S), S)
println("\$index \$value")
end
CartesianIndex{2}((1, 1)) a
CartesianIndex{2}((2, 1)) b
CartesianIndex{2}((1, 2)) d
CartesianIndex{2}((2, 2)) e
```
Note that `enumerate(A)` returns `i` as a *counter* (always starting
at 1), whereas `enumerate(IndexLinear(), A)` returns `i` as an *index*
(starting at the first linear index of `A`, which may or may not be
1).
See also: [`IndexStyle`](@ref), [`indices`](@ref).
"""
enumerate(::IndexLinear, A::AbstractArray) = IndexValue(A, linearindices(A))
enumerate(::IndexCartesian, A::AbstractArray) = IndexValue(A, CartesianRange(indices(A)))
length(v::IndexValue) = length(v.itr)
indices(v::IndexValue) = indices(v.itr)
size(v::IndexValue) = size(v.itr)
@inline start(v::IndexValue) = start(v.itr)
@propagate_inbounds function next(v::IndexValue, state)
indx, n = next(v.itr, state)
item = v.data[indx]
(indx, item), n
end
@inline done(v::IndexValue, state) = done(v.itr, state)
eltype{I,A}(::Type{IndexValue{I,A}}) = Tuple{eltype(I), eltype(A)}
iteratorsize{I}(::Type{IndexValue{I}}) = iteratorsize(I)
iteratoreltype{I}(::Type{IndexValue{I}}) = iteratoreltype(I)
# zip
abstract type AbstractZipIterator end
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()
struct Zip1{I} <: AbstractZipIterator
a::I
end
zip(a) = Zip1(a)
length(z::Zip1) = length(z.a)
size(z::Zip1) = size(z.a)
indices(z::Zip1) = indices(z.a)
eltype{I}(::Type{Zip1{I}}) = Tuple{eltype(I)}
@inline start(z::Zip1) = start(z.a)
@inline function next(z::Zip1, st)
n = next(z.a,st)
return ((n[1],), n[2])
end
@inline done(z::Zip1, st) = done(z.a,st)
iteratorsize{I}(::Type{Zip1{I}}) = iteratorsize(I)
iteratoreltype{I}(::Type{Zip1{I}}) = iteratoreltype(I)
struct Zip2{I1, I2} <: AbstractZipIterator
a::I1
b::I2
end
zip(a, b) = Zip2(a, b)
length(z::Zip2) = _min_length(z.a, z.b, iteratorsize(z.a), iteratorsize(z.b))
size(z::Zip2) = promote_shape(size(z.a), size(z.b))
indices(z::Zip2) = promote_shape(indices(z.a), indices(z.b))
eltype{I1,I2}(::Type{Zip2{I1,I2}}) = Tuple{eltype(I1), eltype(I2)}
@inline start(z::Zip2) = (start(z.a), start(z.b))
@inline function next(z::Zip2, st)
n1 = next(z.a,st[1])
n2 = next(z.b,st[2])
return ((n1[1], n2[1]), (n1[2], n2[2]))
end
@inline done(z::Zip2, st) = done(z.a,st[1]) | done(z.b,st[2])
iteratorsize{I1,I2}(::Type{Zip2{I1,I2}}) = zip_iteratorsize(iteratorsize(I1),iteratorsize(I2))
iteratoreltype{I1,I2}(::Type{Zip2{I1,I2}}) = and_iteratoreltype(iteratoreltype(I1),iteratoreltype(I2))
struct Zip{I, Z<:AbstractZipIterator} <: AbstractZipIterator
a::I
z::Z
end
"""
zip(iters...)
For a set of iterable objects, returns an iterable of tuples, where the `i`th tuple contains
the `i`th component of each input iterable.
Note that [`zip`](@ref) is its own inverse: `collect(zip(zip(a...)...)) == collect(a)`.
```jldoctest
julia> a = 1:5
1:5
julia> b = ["e","d","b","c","a"]
5-element Array{String,1}:
"e"
"d"
"b"
"c"
"a"
julia> c = zip(a,b)
Base.Iterators.Zip2{UnitRange{Int64},Array{String,1}}(1:5, String["e", "d", "b", "c", "a"])
julia> length(c)
5
julia> first(c)
(1, "e")
```
"""
zip(a, b, c...) = Zip(a, zip(b, c...))
length(z::Zip) = _min_length(z.a, z.z, iteratorsize(z.a), iteratorsize(z.z))
size(z::Zip) = promote_shape(size(z.a), size(z.z))
indices(z::Zip) = promote_shape(indices(z.a), indices(z.z))
eltype{I,Z}(::Type{Zip{I,Z}}) = tuple_type_cons(eltype(I), eltype(Z))
@inline start(z::Zip) = tuple(start(z.a), start(z.z))
@inline function next(z::Zip, st)
n1 = next(z.a, st[1])
n2 = next(z.z, st[2])
(tuple(n1[1], n2[1]...), (n1[2], n2[2]))
end
@inline done(z::Zip, st) = done(z.a,st[1]) | done(z.z,st[2])
iteratorsize{I1,I2}(::Type{Zip{I1,I2}}) = zip_iteratorsize(iteratorsize(I1),iteratorsize(I2))
iteratoreltype{I1,I2}(::Type{Zip{I1,I2}}) = and_iteratoreltype(iteratoreltype(I1),iteratoreltype(I2))
# filter
struct Filter{F,I}
flt::F
itr::I
end
filter(flt, itr) = Filter(flt, itr)
start(f::Filter) = start_filter(f.flt, f.itr)
function start_filter(pred, itr)
s = start(itr)
while !done(itr,s)
v,t = next(itr,s)
if pred(v)
return (false, v, t)
end
s=t
end
(true,)
end
next(f::Filter, s) = advance_filter(f.flt, f.itr, s)
function advance_filter(pred, itr, st)
_, v, s = st
while !done(itr,s)
w,t = next(itr,s)
if pred(w)
return v, (false, w, t)
end
s=t
end
v, (true, v, s)
end
done(f::Filter, s) = s[1]
eltype{F,I}(::Type{Filter{F,I}}) = eltype(I)
iteratoreltype{F,I}(::Type{Filter{F,I}}) = iteratoreltype(I)
iteratorsize(::Type{<:Filter}) = SizeUnknown()
# 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`.
"""
rest(itr,state) = Rest(itr,state)
start(i::Rest) = i.st
next(i::Rest, st) = next(i.itr, st)
done(i::Rest, st) = done(i.itr, st)
eltype{I}(::Type{Rest{I}}) = eltype(I)
iteratoreltype{I,S}(::Type{Rest{I,S}}) = iteratoreltype(I)
rest_iteratorsize(a) = SizeUnknown()
rest_iteratorsize(::IsInfinite) = IsInfinite()
iteratorsize{I,S}(::Type{Rest{I,S}}) = rest_iteratorsize(iteratorsize(I))
# Count -- infinite counting
struct Count{S<:Number}
start::S
step::S
end
"""
countfrom(start=1, step=1)
An iterator that counts forever, starting at `start` and incrementing by `step`.
"""
countfrom(start::Number, step::Number) = Count(promote(start, step)...)
countfrom(start::Number) = Count(start, oneunit(start))
countfrom() = Count(1, 1)
eltype{S}(::Type{Count{S}}) = S
start(it::Count) = it.start
next(it::Count, state) = (state, state + it.step)
done(it::Count, state) = false
iteratorsize(::Type{<:Count}) = IsInfinite()
# Take -- iterate through the first n elements
struct Take{I}
xs::I
n::Int
end
"""
take(iter, n)
An iterator that generates at most the first `n` elements of `iter`.
```jldoctest
julia> a = 1:2:11
1:2:11
julia> collect(a)
6-element Array{Int64,1}:
1
3
5
7
9
11
julia> collect(Iterators.take(a,3))
3-element Array{Int64,1}:
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{I}(::Type{Take{I}}) = eltype(I)
iteratoreltype{I}(::Type{Take{I}}) = iteratoreltype(I)
take_iteratorsize(a) = HasLength()
take_iteratorsize(::SizeUnknown) = SizeUnknown()
iteratorsize{I}(::Type{Take{I}}) = take_iteratorsize(iteratorsize(I))
length(t::Take) = _min_length(t.xs, 1:t.n, iteratorsize(t.xs), HasLength())
start(it::Take) = (it.n, start(it.xs))
function next(it::Take, state)
n, xs_state = state
v, xs_state = next(it.xs, xs_state)
return v, (n - 1, xs_state)
end
function done(it::Take, state)
n, xs_state = state
return n <= 0 || done(it.xs, xs_state)
end
# Drop -- iterator through all but the first n elements
struct Drop{I}
xs::I
n::Int
end
"""
drop(iter, n)
An iterator that generates all but the first `n` elements of `iter`.
```jldoctest
julia> a = 1:2:11
1:2:11
julia> collect(a)
6-element Array{Int64,1}:
1
3
5
7
9
11
julia> collect(Iterators.drop(a,4))
2-element Array{Int64,1}:
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{I}(::Type{Drop{I}}) = eltype(I)
iteratoreltype{I}(::Type{Drop{I}}) = iteratoreltype(I)
drop_iteratorsize(::SizeUnknown) = SizeUnknown()
drop_iteratorsize(::Union{HasShape, HasLength}) = HasLength()
drop_iteratorsize(::IsInfinite) = IsInfinite()
iteratorsize{I}(::Type{Drop{I}}) = drop_iteratorsize(iteratorsize(I))
length(d::Drop) = _diff_length(d.xs, 1:d.n, iteratorsize(d.xs), HasLength())
function start(it::Drop)
xs_state = start(it.xs)
for i in 1:it.n
if done(it.xs, xs_state)
break
end
_, xs_state = next(it.xs, xs_state)
end
xs_state
end
next(it::Drop, state) = next(it.xs, state)
done(it::Drop, state) = done(it.xs, state)
# Cycle an iterator forever
struct Cycle{I}
xs::I
end
"""
cycle(iter)
An iterator that cycles through `iter` forever.
"""
cycle(xs) = Cycle(xs)
eltype{I}(::Type{Cycle{I}}) = eltype(I)
iteratoreltype{I}(::Type{Cycle{I}}) = iteratoreltype(I)
iteratorsize{I}(::Type{Cycle{I}}) = IsInfinite()
function start(it::Cycle)
s = start(it.xs)
return s, done(it.xs, s)
end
function next(it::Cycle, state)
s, d = state
if done(it.xs, s)
s = start(it.xs)
end
v, s = next(it.xs, s)
return v, (s, false)
end
done(it::Cycle, state) = state[2]
# 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)`).
```jldoctest
julia> a = Iterators.repeated([1 2], 4);
julia> collect(a)
4-element Array{Array{Int64,2},1}:
[1 2]
[1 2]
[1 2]
[1 2]
```
"""
repeated(x, n::Integer) = take(repeated(x), Int(n))
eltype{O}(::Type{Repeated{O}}) = O
start(it::Repeated) = nothing
next(it::Repeated, state) = (it.x, nothing)
done(it::Repeated, state) = false
iteratorsize(::Type{<:Repeated}) = IsInfinite()
iteratoreltype(::Type{<:Repeated}) = HasEltype()
# Product -- cartesian product of iterators
abstract type AbstractProdIterator end
length(p::AbstractProdIterator) = prod(size(p))
_length(p::AbstractProdIterator) = prod(map(unsafe_length, indices(p)))
size(p::AbstractProdIterator) = _prod_size(p.a, p.b, iteratorsize(p.a), iteratorsize(p.b))
indices(p::AbstractProdIterator) = _prod_indices(p.a, p.b, iteratorsize(p.a), iteratorsize(p.b))
ndims(p::AbstractProdIterator) = length(indices(p))
# generic methods to handle size of Prod* types
_prod_size(a, ::HasShape) = size(a)
_prod_size(a, ::HasLength) = (length(a), )
_prod_size(a, A) =
throw(ArgumentError("Cannot compute size for object of type $(typeof(a))"))
_prod_size(a, b, ::HasLength, ::HasLength) = (length(a), length(b))
_prod_size(a, b, ::HasLength, ::HasShape) = (length(a), size(b)...)
_prod_size(a, b, ::HasShape, ::HasLength) = (size(a)..., length(b))
_prod_size(a, b, ::HasShape, ::HasShape) = (size(a)..., size(b)...)
_prod_size(a, b, A, B) =
throw(ArgumentError("Cannot construct size for objects of types $(typeof(a)) and $(typeof(b))"))
_prod_indices(a, ::HasShape) = indices(a)
_prod_indices(a, ::HasLength) = (OneTo(length(a)), )
_prod_indices(a, A) =
throw(ArgumentError("Cannot compute indices for object of type $(typeof(a))"))
_prod_indices(a, b, ::HasLength, ::HasLength) = (OneTo(length(a)), OneTo(length(b)))
_prod_indices(a, b, ::HasLength, ::HasShape) = (OneTo(length(a)), indices(b)...)
_prod_indices(a, b, ::HasShape, ::HasLength) = (indices(a)..., OneTo(length(b)))
_prod_indices(a, b, ::HasShape, ::HasShape) = (indices(a)..., indices(b)...)
_prod_indices(a, b, A, B) =
throw(ArgumentError("Cannot construct indices for objects of types $(typeof(a)) and $(typeof(b))"))
# one iterator
struct Prod1{I} <: AbstractProdIterator
a::I
end
product(a) = Prod1(a)
eltype{I}(::Type{Prod1{I}}) = Tuple{eltype(I)}
size(p::Prod1) = _prod_size(p.a, iteratorsize(p.a))
indices(p::Prod1) = _prod_indices(p.a, iteratorsize(p.a))
@inline start(p::Prod1) = start(p.a)
@inline function next(p::Prod1, st)
n, st = next(p.a, st)
(n, ), st
end
@inline done(p::Prod1, st) = done(p.a, st)
iteratoreltype{I}(::Type{Prod1{I}}) = iteratoreltype(I)
iteratorsize{I}(::Type{Prod1{I}}) = iteratorsize(I)
# two iterators
struct Prod2{I1, I2} <: AbstractProdIterator
a::I1
b::I2
end
"""
product(iters...)
Returns 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. Example:
```jldoctest
julia> collect(Iterators.product(1:2,3:5))
2×3 Array{Tuple{Int64,Int64},2}:
(1, 3) (1, 4) (1, 5)
(2, 3) (2, 4) (2, 5)
```
"""
product(a, b) = Prod2(a, b)
eltype{I1,I2}(::Type{Prod2{I1,I2}}) = Tuple{eltype(I1), eltype(I2)}
iteratoreltype{I1,I2}(::Type{Prod2{I1,I2}}) = and_iteratoreltype(iteratoreltype(I1),iteratoreltype(I2))
iteratorsize{I1,I2}(::Type{Prod2{I1,I2}}) = prod_iteratorsize(iteratorsize(I1),iteratorsize(I2))
function start(p::AbstractProdIterator)
s1, s2 = start(p.a), start(p.b)
s1, s2, Nullable{eltype(p.b)}(), (done(p.a,s1) || done(p.b,s2))
end
@inline function prod_next(p, st)
s1, s2 = st[1], st[2]
v1, s1 = next(p.a, s1)
nv2 = st[3]
if isnull(nv2)
v2, s2 = next(p.b, s2)
else
v2 = nv2.value
end
if done(p.a, s1)
return (v1,v2), (start(p.a), s2, Nullable{eltype(nv2)}(), done(p.b,s2))
end
return (v1,v2), (s1, s2, Nullable(v2), false)
end
@inline next(p::Prod2, st) = prod_next(p, st)
@inline done(p::AbstractProdIterator, st) = st[4]
# n iterators
struct Prod{I1, I2<:AbstractProdIterator} <: AbstractProdIterator
a::I1
b::I2
end
product(a, b, c...) = Prod(a, product(b, c...))
eltype{I1,I2}(::Type{Prod{I1,I2}}) = tuple_type_cons(eltype(I1), eltype(I2))
iteratoreltype{I1,I2}(::Type{Prod{I1,I2}}) = and_iteratoreltype(iteratoreltype(I1),iteratoreltype(I2))
iteratorsize{I1,I2}(::Type{Prod{I1,I2}}) = prod_iteratorsize(iteratorsize(I1),iteratorsize(I2))
@inline function next{I1,I2}(p::Prod{I1,I2}, st)
x = prod_next(p, st)
((x[1][1],x[1][2]...), x[2])
end
prod_iteratorsize(::Union{HasLength,HasShape}, ::Union{HasLength,HasShape}) = HasShape()
# 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()
# 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. Example:
```jldoctest
julia> collect(Iterators.flatten((1:2, 8:9)))
4-element Array{Int64,1}:
1
2
8
9
```
"""
flatten(itr) = Flatten(itr)
eltype{I}(::Type{Flatten{I}}) = eltype(eltype(I))
iteratorsize{I}(::Type{Flatten{I}}) = SizeUnknown()
iteratoreltype{I}(::Type{Flatten{I}}) = _flatteneltype(I, iteratoreltype(I))
_flatteneltype(I, ::HasEltype) = iteratoreltype(eltype(I))
_flatteneltype(I, et) = EltypeUnknown()
function start(f::Flatten)
local inner, s2
s = start(f.it)
d = done(f.it, s)
# this is a simple way to make this function type stable
d && throw(ArgumentError("argument to Flatten must contain at least one iterator"))
while !d
inner, s = next(f.it, s)
s2 = start(inner)
!done(inner, s2) && break
d = done(f.it, s)
end
return s, inner, s2
end
@inline function next(f::Flatten, state)
s, inner, s2 = state
val, s2 = next(inner, s2)
while done(inner, s2) && !done(f.it, s)
inner, s = next(f.it, s)
s2 = start(inner)
end
return val, (s, inner, s2)
end
@inline function done(f::Flatten, state)
s, inner, s2 = state
return done(f.it, s) && done(inner, s2)
end
"""
partition(collection, n)
Iterate over a collection `n` elements at a time.
```jldoctest
julia> collect(Iterators.partition([1,2,3,4,5], 2))
3-element Array{Array{Int64,1},1}:
[1, 2]
[3, 4]
[5]
```
"""
partition{T}(c::T, n::Integer) = PartitionIterator{T}(c, Int(n))
mutable struct PartitionIterator{T}
c::T
n::Int
end
eltype{T}(::Type{PartitionIterator{T}}) = Vector{eltype(T)}
function length(itr::PartitionIterator)
l = length(itr.c)
return div(l, itr.n) + ((mod(l, itr.n) > 0) ? 1 : 0)
end
start(itr::PartitionIterator) = start(itr.c)
done(itr::PartitionIterator, state) = done(itr.c, state)
function next(itr::PartitionIterator{<:Vector}, state)
l = state
r = min(state + itr.n-1, length(itr.c))
return view(itr.c, l:r), r + 1
end
function next(itr::PartitionIterator, state)
v = Vector{eltype(itr.c)}(itr.n)
i = 0
while !done(itr.c, state) && i < itr.n
i += 1
v[i], state = next(itr.c, state)
end
return resize!(v, i), state
end
end
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