Julia v1.6 Release Notes
========================

New language features
---------------------

* Types written with `where` syntax can now be used to define constructors, e.g.
  `(Foo{T} where T)(x) = ...`.
* `<--` and `<-->` are now available as infix operators, with the same precedence
  and associativity as other arrow-like operators ([#36666]).
* Compilation and type inference can now be enabled or disabled at the module level
  using the experimental macro `Base.Experimental.@compiler_options` ([#37041]).
* The library name passed to `ccall` or `@ccall` can now be an expression involving
  global variables and function calls. The expression will be evaluated the first
  time the `ccall` executes ([#36458]).
* `ꜛ` (U+A71B), `ꜜ` (U+A71C) and `ꜝ` (U+A71D) can now also be used as operator
  suffixes. They can be tab-completed from `\^uparrow`, `\^downarrow` and `\^!` in the REPL
  ([#37542]).
* Standalone "dotted" operators now get parsed as `Expr(:., :op)`, which gets lowered to
  `Base.BroadcastFunction(op)`. This means `.op` is functionally equivalent to
  `(x...) -> (op).(x...)`, which can be useful for passing the broadcasted version of an
  operator to higher-order functions, for example `map(.*, A, B)` for an elementwise
  product of two arrays of arrays ([#37583]).
* The syntax `import A as B` (plus `import A: x as y`, `import A.x as y`, and `using A: x as y`)
  can now be used to rename imported modules and identifiers ([#1255]).
* Unsigned literals (starting with `0x`) which are too big to fit in a `UInt128` object
  are now interpreted as `BigInt` ([#23546]).
* It is now possible to use `...` on the left-hand side of assignments for taking any
  number of items from the front of an iterable collection, while also collecting the rest,
  for example `a, b... = [1, 2, 3]`. This syntax is implemented using `Base.rest`,
  which can be overloaded to customize its behavior for different collection types
  ([#37410]).

Language changes
----------------

* The postfix conjugate transpose operator `'` now accepts Unicode modifiers as
  suffixes, so e.g. `a'ᵀ` is parsed as `var"'ᵀ"(a)`, which can be defined by the
  user. `a'ᵀ` parsed as `a' * ᵀ` before, so this is a minor breaking change ([#37247]).
* Macros that return `:quote` expressions (e.g. via `Expr(:quote, ...)`) were previously
  able to work without escaping (`esc(...)`) their output when needed. This has been
  corrected, and now `esc` must be used in these macros as it is in other macros ([#37540]).
* The `-->` operator now lowers to a `:call` expression, so it can be defined as
  a function like other operators. The dotted version `.-->` is now parsed as well.
  For backwards compatibility, `-->` still parses using its own expression head
  instead of `:call`.
* `⌿` (U+233F) and `¦` (U+00A6) are now infix operators with times-like and plus-like precedence,
  respectively. Previously they were parsed as identifier characters ([#37973]).

Compiler/Runtime improvements
-----------------------------

* All platforms can now use `@executable_path` within `jl_load_dynamic_library()`.
  This allows executable-relative paths to be embedded within executables on all
  platforms, not just MacOS, which the syntax is borrowed from ([#35627]).
* Constant propagation now occurs through keyword arguments ([#35976]).
* The precompilation cache is now created atomically ([#36416]). Invoking _n_
  Julia processes simultaneously may create _n_ temporary caches.

Command-line option changes
---------------------------

* There is no longer a concept of "home project": starting `julia --project=dir`
  is now exactly equivalent to starting `julia` and then doing `pkg> activate
  $dir` and `julia --project` is exactly equivalent to doing that where
  `dir = Base.current_project()`. In particular, this means that if you do
  `pkg> activate` after starting `julia` with the `--project` option (or with
  `JULIA_PROJECT` set) it will take you to the default active project, which is
  `@v1.5` unless you have modified `LOAD_PATH` ([#36434]).

Multi-threading changes
-----------------------


Build system changes
--------------------

* Windows Installer now has the option to 'Add Julia to Path'. To unselect this option
  from the commandline simply remove the tasks you do not want to be installed: e.g.
  `./julia-installer.exe /TASKS="desktopicon,startmenu,addtopath"`, adds a desktop
  icon, a startmenu group icon, and adds Julia to system PATH.

New library functions
---------------------

* New function `Base.kron!` and corresponding overloads for various matrix types for performing Kronecker product in-place ([#31069]).
* New function `Base.Threads.foreach(f, channel::Channel)` for multithreaded `Channel` consumption ([#34543]).
* New function `Base.readeach(io, T)` for iteratively performing `read(io, T)` ([#36150]).
* `Iterators.map` is added. It provides another syntax `Iterators.map(f, iterators...)`
  for writing `(f(args...) for args in zip(iterators...))`, i.e. a lazy `map` ([#34352]).
* New function `sincospi` for simultaneously computing `sinpi(x)` and `cospi(x)` more
  efficiently ([#35816]).
* New function `addenv` for adding environment mappings into a `Cmd` object, returning the new `Cmd` object.
* New function `insorted` for determining whether an element is in a sorted collection or not ([#37490]).
* New function `Base.rest` for taking the rest of a collection, starting from a specific
  iteration state, in a generic way ([#37410]).

New library features
--------------------

* `findfirst`, `findnext`, `findlast`, and `findall` now support `AbstractVector{<:Union{Int8,UInt8}}` (pattern, array) arguments ([#37283]).
* The `redirect_*` functions can now be called on `IOContext` objects.
* New constructor `NamedTuple(iterator)` that constructs a named tuple from a key-value pair iterator.
* A new `reinterpret(reshape, T, a::AbstractArray{S})` reinterprets `a` to have eltype `T` while potentially
  inserting or consuming the first dimension depending on the ratio of `sizeof(T)` and `sizeof(S)`.
* New `append!(vector, collections...)` and `prepend!(vector, collections...)` methods accept multiple
  collections to be appended or prepended ([#36227]).
* The postfix operator `'ᵀ` can now be used as an alias for `transpose` ([#38062]).
* `keys(io::IO)` has been added, which returns all keys of `io` if `io` is an `IOContext` and an empty
  `Base.KeySet` otherwise ([#37753]).
* `count` now accepts an optional `init` argument to control the accumulation type ([#37461]).

Standard library changes
------------------------

* `pkg> precompile` is now parallelized through depth-first precompilation of dependencies. Errors will only throw for
  direct dependencies listed in the `Project.toml`.
* `pkg> precompile` is now automatically triggered whenever Pkg changes the active manifest. Auto-precompilation will
  remember if a package has errored within the given environment and will not retry until it changes.
  Auto-precompilation can be gracefully interrupted with a `ctrl-c` and disabled by setting the environment variable
  `JULIA_PKG_PRECOMPILE_AUTO=0`.
* The `nextprod` function now accepts tuples and other array types for its first argument ([#35791]).
* The `reverse(A; dims)` function for multidimensional `A` can now reverse multiple dimensions at once
  by passing a tuple for `dims`, and defaults to reversing all dimensions; there is also a multidimensional
  in-place `reverse!(A; dims)` ([#37367]).
* The function `isapprox(x,y)` now accepts the `norm` keyword argument also for numeric (i.e., non-array) arguments `x` and `y` ([#35883]).
* `ispow2(x)` now supports non-`Integer` arguments `x` ([#37635]).
* `view`, `@view`, and `@views` now work on `AbstractString`s, returning a `SubString` when appropriate ([#35879]).
* All `AbstractUnitRange{<:Integer}`s now work with `SubString`, `view`, `@view` and `@views` on strings ([#35879]).
* `sum`, `prod`, `maximum`, and `minimum` now support `init` keyword argument ([#36188], [#35839]).
* `unique(f, itr; seen=Set{T}())` now allows you to declare the container type used for
  keeping track of values returned by `f` on elements of `itr` ([#36280]).
* `Libdl` has been moved to `Base.Libc.Libdl`, however it is still accessible as an stdlib ([#35628]).
* `first` and `last` functions now accept an integer as second argument to get that many
  leading or trailing elements of any iterable ([#34868]).
* `intersect` on `CartesianIndices` now returns `CartesianIndices` instead of `Vector{<:CartesianIndex}` ([#36643]).
* `CartesianIndices` now supports step different from `1`. It can also be constructed from three
  `CartesianIndex`es `I`, `S`, `J` using `I:S:J`. `step` for `CartesianIndices` now returns a
  `CartesianIndex` ([#37829]).
* `push!(c::Channel, v)` now returns channel `c`. Previously, it returned the pushed value `v` ([#34202]).
* `RegexMatch` objects can now be probed for whether a named capture group exists within it through `haskey()` ([#36717]).
* For consistency `haskey(r::RegexMatch, i::Integer)` has also been added and returns if the capture group for `i` exists ([#37300]).
* A new standard library `TOML` has been added for parsing and printing [TOML files](https://toml.io) ([#37034]).
* The composition operator `∘` now returns a `Base.ComposedFunction` instead of an anonymous function ([#37517]).
* A new standard library `Downloads` has been added, which replaces the old `Base.download` function with `Downloads.download`, providing cross-platform, multi-protocol, in-process download functionality implemented with [libcurl](https://curl.haxx.se/libcurl/) ([#37340]).
* The `Pkg.BinaryPlatforms` module has been moved into `Base` as `Base.BinaryPlatforms` and heavily reworked.
  Applications that want to be compatible with the old API should continue to import `Pkg.BinaryPlatforms`,
  however new users should use `Base.BinaryPlatforms` directly ([#37320]).
* Logging (such as `@warn`) no longer catches exceptions in the logger itself ([#36600]).
* The `Pkg.Artifacts` module has been imported as a separate standard library.  It is still available as
  `Pkg.Artifacts`, however starting from Julia v1.6+, packages may import simply `Artifacts` without importing
  all of `Pkg` alongside ([#37320]).
* `@time` now reports if the time presented included any compilation time, which is shown as a percentage ([#37678]).
* `@varinfo` can now report non-exported objects within modules, look recursively into submodules, and return a sorted
  results table ([#38042]).
* `@testset` now supports the option `verbose` to show the test result summary
  of the children even if they all pass ([#33755]).

#### LinearAlgebra

* New method `LinearAlgebra.issuccess(::CholeskyPivoted)` for checking whether pivoted Cholesky factorization was successful ([#36002]).
* `UniformScaling` can now be indexed into using ranges to return dense matrices and vectors ([#24359]).
* New function `LinearAlgebra.BLAS.get_num_threads()` for getting the number of BLAS threads ([#36360]).
* `(+)(::UniformScaling)` is now defined, making `+I` a valid unary operation ([#36784]).
* Instances of `UniformScaling` are no longer `isequal` to matrices. Previous
  behaviour violated the rule that `isequal(x, y)` implies `hash(x) == hash(y)`.

#### Markdown

#### Printf

* Complete overhaul of internal code to use the ryu float printing algorithms (from Julia 1.4); leads to consistent 2-5x performance improvements.
* New `Printf.tofloat` function allowing custom float types to more easily integrate with Printf formatting by converting their type to `Float16`, `Float32`, `Float64`, or `BigFloat`.
* New `Printf.format"..."` and `Printf.Format(...)` functions that allow creating `Printf.Format` objects that can be passed to `Printf.format` for easier dynamic printf formatting.
* `Printf.format(f::Printf.Format, args...)` as a non-macro function that applies a printf format `f` to provided `args`.

#### Random


#### REPL

* The `AbstractMenu` extension interface of `REPL.TerminalMenus` has been extensively
  overhauled. The new interface does not rely on global configuration variables, is more
  consistent in delegating printing of the navigation/selection markers, and provides
  improved support for dynamic menus.  These changes are compatible with the previous
  (deprecated) interface, so are non-breaking.

  The new API offers several enhancements:

  + Menus are configured in their constructors via keyword arguments.
  + For custom menu types, the new `Config` and `MultiSelectConfig` replace the global `CONFIG` `Dict`.
  + `request(menu; cursor=1)` allows you to control the initial cursor position in the menu (defaults to first item).
  + `MultiSelectMenu` allows you to pass a list of initially-selected items with the `selected` keyword argument.
  + `writeLine` was deprecated to `writeline`, and `writeline` methods are not expected to print the cursor indicator.
    The old `writeLine` continues to work, and any of its method extensions should print the cursor indicator as before.
  + `printMenu` has been deprecated to `printmenu`, and it both accepts a state input and returns a state output
    that controls the number of terminal lines erased when the menu is next refreshed. This plus related changes
    makes `printmenu` work properly when the number of menu items might change depending on user choices.
  + `numoptions`, returning the number of items in the menu, has been added as an alternative to implementing `options`.
  + `suppress_output` (primarily a testing option) has been added as a keyword argument to `request`,
    rather than a configuration option.

* Windows REPL now supports 24-bit colors, by correctly interpreting virtual terminal escapes.

#### SparseArrays

* Display large sparse matrices with a Unicode "spy" plot of their nonzero patterns,
  and display small sparse matrices by an `Matrix`-like 2d layout of their contents.
* New convenient `spdiagm([m, n,] v::AbstractVector)` methods which call
  `spdiagm([m, n,] 0 => v)`, consistently with their dense `diagm` counterparts ([#37684]).

#### Dates

* `Quarter` period is defined ([#35519]).
* `canonicalize` can now take `Period` as an input ([#37391]).
* Zero-valued `FixedPeriod`s and `OtherPeriod`s now compare equal, e.g.,
  `Year(0) == Day(0)`. The behavior of non-zero `Period`s is not changed ([#37486]).

#### Statistics


#### Sockets


#### Distributed


#### UUIDs

* Change `uuid1` and `uuid4` to use `Random.RandomDevice()` as default random number generator ([#35872]).
* Added `parse(::Type{UUID}, ::AbstractString)` method.

#### Mmap

* On Unix systems, the `Mmap.madvise!` function (along with OS-specific `Mmap.MADV_*`
  constants) has been added to give advice on handling of memory-mapped arrays ([#37369]).

Deprecated or removed
---------------------

* The `Base.download` function has been deprecated (silently, by default) in favor of the new `Downloads.download` standard library function ([#37340]).
* The `Base.Grisu` code has been officially removed (float printing was switched to the ryu algorithm code in 1.4).
  The code is available from [JuliaAttic](https://github.com/JuliaAttic/Grisu.jl) if needed.

External dependencies
---------------------


Tooling Improvements
---------------------


<!--- generated by NEWS-update.jl: -->
[#1255]: https://github.com/JuliaLang/julia/issues/1255
[#23546]: https://github.com/JuliaLang/julia/issues/23546
[#24359]: https://github.com/JuliaLang/julia/issues/24359
[#31069]: https://github.com/JuliaLang/julia/issues/31069
[#34202]: https://github.com/JuliaLang/julia/issues/34202
[#34352]: https://github.com/JuliaLang/julia/issues/34352
[#34543]: https://github.com/JuliaLang/julia/issues/34543
[#34868]: https://github.com/JuliaLang/julia/issues/34868
[#35519]: https://github.com/JuliaLang/julia/issues/35519
[#35627]: https://github.com/JuliaLang/julia/issues/35627
[#35628]: https://github.com/JuliaLang/julia/issues/35628
[#35791]: https://github.com/JuliaLang/julia/issues/35791
[#35816]: https://github.com/JuliaLang/julia/issues/35816
[#35839]: https://github.com/JuliaLang/julia/issues/35839
[#35872]: https://github.com/JuliaLang/julia/issues/35872
[#35879]: https://github.com/JuliaLang/julia/issues/35879
[#35883]: https://github.com/JuliaLang/julia/issues/35883
[#35976]: https://github.com/JuliaLang/julia/issues/35976
[#36002]: https://github.com/JuliaLang/julia/issues/36002
[#36150]: https://github.com/JuliaLang/julia/issues/36150
[#36188]: https://github.com/JuliaLang/julia/issues/36188
[#36227]: https://github.com/JuliaLang/julia/issues/36227
[#36280]: https://github.com/JuliaLang/julia/issues/36280
[#36360]: https://github.com/JuliaLang/julia/issues/36360
[#36416]: https://github.com/JuliaLang/julia/issues/36416
[#36434]: https://github.com/JuliaLang/julia/issues/36434
[#36458]: https://github.com/JuliaLang/julia/issues/36458
[#36600]: https://github.com/JuliaLang/julia/issues/36600
[#36643]: https://github.com/JuliaLang/julia/issues/36643
[#36666]: https://github.com/JuliaLang/julia/issues/36666
[#36717]: https://github.com/JuliaLang/julia/issues/36717
[#36784]: https://github.com/JuliaLang/julia/issues/36784
[#37034]: https://github.com/JuliaLang/julia/issues/37034
[#37041]: https://github.com/JuliaLang/julia/issues/37041
[#37247]: https://github.com/JuliaLang/julia/issues/37247
[#37283]: https://github.com/JuliaLang/julia/issues/37283
[#37300]: https://github.com/JuliaLang/julia/issues/37300
[#37320]: https://github.com/JuliaLang/julia/issues/37320
[#37340]: https://github.com/JuliaLang/julia/issues/37340
[#37367]: https://github.com/JuliaLang/julia/issues/37367
[#37369]: https://github.com/JuliaLang/julia/issues/37369
[#37391]: https://github.com/JuliaLang/julia/issues/37391
[#37410]: https://github.com/JuliaLang/julia/issues/37410
[#37461]: https://github.com/JuliaLang/julia/issues/37461
[#37486]: https://github.com/JuliaLang/julia/issues/37486
[#37490]: https://github.com/JuliaLang/julia/issues/37490
[#37517]: https://github.com/JuliaLang/julia/issues/37517
[#37540]: https://github.com/JuliaLang/julia/issues/37540
[#37542]: https://github.com/JuliaLang/julia/issues/37542
[#37583]: https://github.com/JuliaLang/julia/issues/37583
[#37635]: https://github.com/JuliaLang/julia/issues/37635
[#37678]: https://github.com/JuliaLang/julia/issues/37678
[#37684]: https://github.com/JuliaLang/julia/issues/37684
[#37753]: https://github.com/JuliaLang/julia/issues/37753
[#37829]: https://github.com/JuliaLang/julia/issues/37829
[#37973]: https://github.com/JuliaLang/julia/issues/37973
[#38042]: https://github.com/JuliaLang/julia/issues/38042
[#38062]: https://github.com/JuliaLang/julia/issues/38062