# Julia v1.5 Release Notes

## New language features

- Macro calls `@foo {...}` can now also be written `@foo{...}` (without the space) (#34498).
- `⨟` is now parsed as a binary operator with times precedence. It can be entered in the REPL with `\bbsemi` followed by <kbd>TAB</kbd> (#34722).
- `±` and `∓` are now unary operators as well, like `+` or `-`. Attention has to be paid in macros and matrix constructors, which are whitespace sensitive, because expressions like `[a ±b]` now get parsed as `[a ±(b)]` instead of `[±(a, b)]` (#34200).
- Passing an identifier `x` by itself as a keyword argument or named tuple element is equivalent to `x=x`, implicitly using the name of the variable as the keyword or named tuple field name. Similarly, passing an `a.b` expression uses `b` as the keyword or field name (#29333).
- Support for Unicode 13.0.0 (via utf8proc 2.5) (#35282).
- The compiler optimization level can now be set per-module using the experimental macro `Base.Experimental.@optlevel n`. For code that is not performance-critical, setting this to 0 or 1 can provide significant latency improvements (#34896).

## Language changes

- The interactive REPL now uses "soft scope" for top-level expressions: an assignment inside a scope block such as a `for` loop automatically assigns to a global variable if one has been defined already. This matches the behavior of Julia versions 0.6 and prior, as well as IJulia. Note that this only affects expressions interactively typed or pasted directly into the default REPL (#28789, #33864).
- Outside of the REPL (e.g. in a file), assigning to a variable within a top-level scope block is considered ambiguous if a global variable with the same name exists. A warning is given if that happens, to alert you that the code will work differently than in the REPL. A new command line option `--warn-scope` controls this warning (#33864).
- Converting arbitrary tuples to `NTuple`, e.g. `convert(NTuple, (1, ""))` now gives an error, where it used to be incorrectly allowed. This is because `NTuple` refers only to homogeneous tuples (this meaning has not changed) (#34272).
- The syntax `(;)` (which was deprecated in v1.4) now creates an empty named tuple (#30115).
- `@inline` macro can now be applied to short-form anonymous functions (#34953).
- In triple-quoted string literals, whitespace stripping is now done before processing escape sequences instead of after. For example, the syntax

      """
        a\n b"""

  used to yield the string " a\nb", since the single space before `b` set the indent level. Now the result is "a\n b", since the space before `b` is no longer considered to occur at the start of a line. The old behavior is considered a bug (#35001).
- `<:` and `>:` can now be broadcasted over arrays with `.<:` and `.>:` (#35085)
- The line number of function definitions is now added by the parser as an additional `LineNumberNode` at the start of each function body (#35138).
- Statements of the form `a'` now get lowered to `var"'"(a)` instead of `Base.adjoint(a)`. This allows for shadowing this function in local scopes, although this is generally discouraged. By default, Base exports `var"'"` as an alias of `Base.adjoint`, so custom types should still extend `Base.adjoint` (#34634).

## Compiler/Runtime improvements

- Immutable structs (including tuples) that contain references can now be allocated on the stack, and allocated inline within arrays and other structs (#33886). This significantly reduces the number of heap allocations in some workloads. Code that requires assumptions about object layout and addresses (usually for interoperability with C or other languages) might need to be updated; for example any object that needs a stable address should be a `mutable struct`. As a result, Array `view`s no longer allocate (#34126).

## Command-line option changes

- Deprecation warnings are no longer shown by default. i.e. if the `--depwarn=...` flag is not passed it defaults to `--depwarn=no`. The warnings are printed from tests run by `Pkg.test()` (#35362).
- Color now defaults to on when stdout and stderr are TTYs (#34347).
- `-t N`, `--threads N` starts Julia with `N` threads. This option takes precedence over `JULIA_NUM_THREADS`. The specified number of threads also propagates to worker processes spawned using the `-p`/`--procs` or `--machine-file` command line arguments. In order to set number of threads for worker processes spawned with `addprocs` use the `exeflags` keyword argument, e.g. `addprocs(...; exeflags=`--threads 4`)` (#35108).

## Multi-threading changes

- Parts of the multi-threading API are now considered stable, with caveats. This includes all documented identifiers from `Base.Threads` except the `atomic_` operations.
- `@threads` now allows an optional schedule argument. Use `@threads :static ...` to ensure that the same schedule will be used as in past versions; the default schedule is likely to change in the future.

## Build system changes

- The build system now contains a pure-make caching system for expanding expensive operations at the latest possible moment, while still expanding it only once (#35626).

## New library functions

- Packages can now provide custom hints to help users resolve errors by using the experimental `Base.Experimental.register_error_hint` function. Packages that define custom exception types can support hints by calling the `Base.Experimental.show_error_hints` from their `showerror` method (#35094).
- The `@ccall` macro has been added to Base. It is a near drop-in replacement for `ccall` with more Julia-like syntax. It also wraps the new `foreigncall` API for varargs of different types, though it lacks the capability to specify an LLVM calling convention (#32748).
- New functions `mergewith` and `mergewith!` supersede `merge` and `merge!` with `combine` argument. They don't have the restriction for `combine` to be a `Function` and also provide one-argument method that returns a closure. The old methods of `merge` and `merge!` are still available for backward compatibility (#34296).
- The new `isdisjoint` function indicates whether two collections are disjoint (#34427).
- Add function `ismutable` and deprecate `isimmutable` to check whether something is mutable (#34652).
- `include` now accepts an optional `mapexpr` first argument to transform the parsed expressions before they are evaluated (#34595).
- New function `bitreverse` for reversing the order of bits in a fixed-width integer (#34791).
- New function `bitrotate(x, k)` for rotating the bits in a fixed-width integer (#33937).
- New function `contains(haystack, needle)` and its one argument partially applied form have been added, it acts like `occursin(needle, haystack)` (#35132).
- New function `Base.exit_on_sigint` is added to control if `InterruptException` is thrown by Ctrl-C (#29411).
- New function `popat!(vector, index, [default])` for removing an element at an arbitrary index from a `Vector` (#35513, #36070).

## New library features

- Function composition now works also on one argument `∘(f) = f` (#34251).
- One argument methods `startswith(x)` and `endswith(x)` have been added, returning partially-applied versions of the functions, similar to existing methods like `isequal(x)` (#33193).
- `isapprox` (or `≈`) now has a one-argument "curried" method `isapprox(x)` which returns a function, like `isequal` (or `==`) (#32305).
- `@NamedTuple{key1::Type1, ...}` macro for convenient `NamedTuple` declarations (#34548).
- `Ref{NTuple{N,T}}` can be passed to `Ptr{T}`/`Ref{T}` `ccall` signatures (#34199).
- `x::Signed % Unsigned` and `x::Unsigned % Signed` are supported for integer bitstypes.
- `signed(unsigned_type)` is supported for integer bitstypes, `unsigned(signed_type)` has been supported.
- `accumulate`, `cumsum`, and `cumprod` now support `Tuple` (#34654) and arbitrary iterators (#34656).
- In `splice!` with no replacement, values to be removed can now be specified with an arbitrary iterable (instead of a `UnitRange`) (#34524).
- The `@view` and `@views` macros now support the `a[begin]` syntax that was introduced in Julia 1.4 (#35289).
- `open` for files now accepts a keyword argument `lock` controlling whether file operations will acquire locks for safe multi-threaded access. Setting it to `false` provides better performance when only one thread will access the file (#35426).
- The introspection macros (`@which`, `@code_typed`, etc.) now work with `do`-block syntax (#35283) and with dot syntax (#35522).
- `count` now accepts the `dims` keyword.
- new in-place `count!` function similar to `sum!`.
- `peek` is now exported and accepts a type to peek from a stream (#28811).

## Standard library changes

- Empty ranges now compare equal, regardless of their startpoint and step (#32348).
- A 1-d `Zip` iterator (where `Base.IteratorSize` is `Base.HasShape{1}()`) with defined length of `n` has now also size of `(n,)` (instead of throwing an error with truncated iterators) (#29927).
- The `@timed` macro now returns a `NamedTuple` (#34149).
- New `supertypes(T)` function returns a tuple of all supertypes of `T` (#34419).
- Views of builtin ranges are now recomputed ranges (like indexing returns) instead of `SubArray`s (#26872).
- Sorting-related functions such as `sort` that take the keyword arguments `lt`, `rev`, `order` and `by` now do not discard `order` if `by` or `lt` are passed. In the former case, the order from `order` is used to compare the values of `by(element)`. In the latter case, any order different from `Forward` or `Reverse` will raise an error about the ambiguity.
- `close` on a file (`IOStream`) can now throw an exception if an error occurs when trying to flush buffered data to disk (#35303).
- The large `StridedArray` `Union` now has special printing to avoid printing out its entire contents (#31149).

#### LinearAlgebra

- The BLAS submodule now supports the level-2 BLAS subroutine `hpmv!` (#34211).
- `normalize` now supports multidimensional arrays (#34239).
- `lq` factorizations can now be used to compute the minimum-norm solution to under-determined systems (#34350).
- `sqrt(::Hermitian)` now treats slightly negative eigenvalues as zero for nearly semidefinite matrices, and accepts a new `rtol` keyword argument for this tolerance (#35057).
- The BLAS submodule now supports the level-2 BLAS subroutine `spmv!` (#34320).
- The BLAS submodule now supports the level-1 BLAS subroutine `rot!` (#35124).
- New generic `rotate!(x, y, c, s)` and `reflect!(x, y, c, s)` functions (#35124).

#### Markdown

- In docstrings, a level-1 markdown header "Extended help" is now interpreted as a marker dividing "brief help" from "extended help". The REPL help mode only shows the brief help (the content before the "Extended help" header) by default; prepend the expression with '?' (in addition to the one that enters the help mode) to see the full docstring (#25930).

#### Random

- `randn!(::MersenneTwister, ::Array{Float64})` is faster, and as a result, for a given state of the RNG, the corresponding generated numbers have changed (#35078).
- `rand!(::MersenneTwister, ::Array{Bool})` is faster, and as a result, for a given state of the RNG, the corresponding generated numbers have changed (#33721).
- A new faster algorithm ("nearly division less") is used for generating random numbers within a range (#29240). As a result, the streams of generated numbers are changed (for ranges, like in `rand(1:9)`, and for collections in general, like in `rand([1, 2, 3])`). Also, for performance, the undocumented property that, given a seed and `a, b` of type `Int`, `rand(a:b)` produces the same stream on 32 and 64 bits architectures, is dropped.

#### REPL

#### SparseArrays

- `lu!` accepts `UmfpackLU` as an argument to make use of its symbolic factorization.
- The `trim` keyword argument for the functions `fkeep!`, `tril!`, `triu!`, `droptol!`,`dropzeros!` and `dropzeros` has been removed in favour of always trimming. Calling these with `trim=false` could result in invalid sparse arrays.

#### Dates

- The `eps` function now accepts `TimeType` types (#31487).
- The `zero` function now accepts `TimeType` types (#35554).

#### Statistics

#### Sockets

- Joining and leaving UDP multicast groups on a `UDPSocket` is now supported through `join_multicast_group()` and `leave_multicast_group()` (#35521).

#### Distributed

- `launch_on_machine` now supports and parses ipv6 square-bracket notation (#34430).

## Deprecated or removed

## External dependencies

- OpenBLAS has been updated to v0.3.9 (#35113).

## Tooling Improvements

Theme

This document was generated with Documenter.jl on Thursday 24 September 2020. Using Julia version 1.5.2.