# 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`.
- The `a[begin, k]` syntax now calls `firstindex(a, 1)` rather than `first(axes(a, 1))` (#35779), but the former now defaults to the latter for any `a` (#38742).
- `⌿` (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 `@v1.6` unless you have modified `LOAD_PATH` (#36434).

## Multi-threading changes

- Locks now automatically inhibit finalizers from running, to avoid deadlock (#38487).
- New function `Base.Threads.foreach(f, channel::Channel)` for multithreaded `Channel` consumption (#34543).
- There is no longer a restriction on the number of threads (#36778).

## 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.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 `cispi(x)` for more accurately computing `cis(pi * x)` (#38449).
- 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

- The `redirect_*` functions now accept `devnull` to discard all output redirected to it, and as an empty input (#36146).
- The `redirect_*` functions can now be called on `IOContext` objects (#36688).
- `findfirst`, `findnext`, `findlast`, and `findall` now support `AbstractVector{<:Union{Int8,UInt8}}` (pattern, array) arguments (#37283).
- 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).
- New method `occursin(haystack)` that returns a function that checks whether its argument occurs in `haystack` (#38475).
- New methods `∉(collection)`, `∋(item)`, and `∌(item)` returning corresponding containment-testing functions (#38475).
- 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).
- `first` and `last` functions now accept an integer as second argument to get that many leading or trailing elements of any iterable (#34868).
- `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).
- `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).

## Standard library changes

- A new standard library `TOML` has been added for parsing and printing TOML files (#37034).
- 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 (#37340).
- `Libdl` has been moved to `Base.Libc.Libdl`, however it is still accessible as an stdlib (#35628).
- To download artifacts lazily, `LazyArtifacts` now must be explicitly listed as a dependency, to avoid needing the support machinery to be available when it is not commonly needed (#37844).
- It is no longer possible to create a `LinRange`, `StepRange`, or `StepRangeLen` with a `<: Integer` eltype but non-integer step (#32439).
- `intersect` on `CartesianIndices` now returns `CartesianIndices` instead of `Vector{<:CartesianIndex}` (#36643).
- `push!(c::Channel, v)` now returns channel `c`. Previously, it returned the pushed value `v` (#34202).
- The composition operator `∘` now returns a `Base.ComposedFunction` instead of an anonymous function (#37517).
- Logging (such as `@warn`) no longer catches exceptions in the logger itself (#36600).
- `@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).
- In `LinearIndices(::Tuple)` and `CartesianIndices(::Tuple)`, integers (as opposed to ranges of integers) in the argument tuple now consistently describe 1-based ranges, e.g, `CartesianIndices((3, 1:3))` is equivalent to `CartesianIndices((1:3, 1:3))`. This is how tuples of integers have always been documented to work, but a bug had caused erroneous behaviors with heterogeneous tuples containing both integers and ranges (#37829, #37928).

#### Package Manager

- `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 `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).
- 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).

#### 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)`.
- Transposing `*Triangular` matrices now returns matrices of the opposite triangular type, consistently with `adjoint!(::*Triangular)` and `transpose!(::*Triangular)`. Packages containing methods with, e.g., `Adjoint{<:Any,<:LowerTriangular{<:Any,<:OwnMatrixType}}` should replace that by `UpperTriangular{<:Any,<:Adjoint{<:Any,<:OwnMatrixType}}` in the method signature (#38168).

#### 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.

- Tab completion now supports runs of consecutive sub/superscript characters, e.g. `\^(3)` tab-completes to `⁽³⁾` (#38649).

- 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 (#33821).
- 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

- Now supports invoking Windows workers via ssh (via new keyword argument `shell=:wincmd` in `addprocs`) (#30614).
- Other new keyword arguments in `addprocs`: `ssh` to specify the ssh client path, `env` to pass environment variables to workers, and `cmdline_cookie` to work around an ssh problem with Windows workers that run older (pre-ConPTY) versions of Windows, Julia or OpenSSH (#30614).

#### 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 if needed.

## External dependencies

## Tooling Improvements

Theme

This document was generated with Documenter.jl on Tuesday 16 March 2021. Using Julia version 1.6.0-rc3.