========================
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](https://github.com/JuliaLang/IJulia.jl).
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 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]).
* `pop!(collection, key, [default])` now has a method for `Vector` to remove an element at an arbitrary index ([35513]).
* 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
---------------------
<!--- generated by NEWS-update.jl: -->
[25930]: https://github.com/JuliaLang/julia/issues/25930
[26872]: https://github.com/JuliaLang/julia/issues/26872
[28789]: https://github.com/JuliaLang/julia/issues/28789
[29240]: https://github.com/JuliaLang/julia/issues/29240
[29333]: https://github.com/JuliaLang/julia/issues/29333
[29411]: https://github.com/JuliaLang/julia/issues/29411
[29927]: https://github.com/JuliaLang/julia/issues/29927
[30115]: https://github.com/JuliaLang/julia/issues/30115
[31149]: https://github.com/JuliaLang/julia/issues/31149
[31487]: https://github.com/JuliaLang/julia/issues/31487
[32305]: https://github.com/JuliaLang/julia/issues/32305
[32348]: https://github.com/JuliaLang/julia/issues/32348
[32748]: https://github.com/JuliaLang/julia/issues/32748
[33193]: https://github.com/JuliaLang/julia/issues/33193
[33721]: https://github.com/JuliaLang/julia/issues/33721
[33864]: https://github.com/JuliaLang/julia/issues/33864
[33886]: https://github.com/JuliaLang/julia/issues/33886
[33937]: https://github.com/JuliaLang/julia/issues/33937
[34149]: https://github.com/JuliaLang/julia/issues/34149
[34199]: https://github.com/JuliaLang/julia/issues/34199
[34200]: https://github.com/JuliaLang/julia/issues/34200
[34211]: https://github.com/JuliaLang/julia/issues/34211
[34239]: https://github.com/JuliaLang/julia/issues/34239
[34272]: https://github.com/JuliaLang/julia/issues/34272
[34296]: https://github.com/JuliaLang/julia/issues/34296
[34320]: https://github.com/JuliaLang/julia/issues/34320
[34347]: https://github.com/JuliaLang/julia/issues/34347
[34350]: https://github.com/JuliaLang/julia/issues/34350
[34419]: https://github.com/JuliaLang/julia/issues/34419
[34427]: https://github.com/JuliaLang/julia/issues/34427
[34430]: https://github.com/JuliaLang/julia/issues/34430
[34498]: https://github.com/JuliaLang/julia/issues/34498
[34524]: https://github.com/JuliaLang/julia/issues/34524
[34548]: https://github.com/JuliaLang/julia/issues/34548
[34595]: https://github.com/JuliaLang/julia/issues/34595
[34634]: https://github.com/JuliaLang/julia/issues/34634
[34652]: https://github.com/JuliaLang/julia/issues/34652
[34654]: https://github.com/JuliaLang/julia/issues/34654
[34656]: https://github.com/JuliaLang/julia/issues/34656
[34722]: https://github.com/JuliaLang/julia/issues/34722
[34791]: https://github.com/JuliaLang/julia/issues/34791
[34896]: https://github.com/JuliaLang/julia/issues/34896
[34953]: https://github.com/JuliaLang/julia/issues/34953
[35001]: https://github.com/JuliaLang/julia/issues/35001
[35078]: https://github.com/JuliaLang/julia/issues/35078
[35094]: https://github.com/JuliaLang/julia/issues/35094
[35108]: https://github.com/JuliaLang/julia/issues/35108
[35124]: https://github.com/JuliaLang/julia/issues/35124
[35132]: https://github.com/JuliaLang/julia/issues/35132
[35138]: https://github.com/JuliaLang/julia/issues/35138
[35282]: https://github.com/JuliaLang/julia/issues/35282
[35283]: https://github.com/JuliaLang/julia/issues/35283
[35289]: https://github.com/JuliaLang/julia/issues/35289
[35303]: https://github.com/JuliaLang/julia/issues/35303
[35362]: https://github.com/JuliaLang/julia/issues/35362
[35426]: https://github.com/JuliaLang/julia/issues/35426
[35513]: https://github.com/JuliaLang/julia/issues/35513
[35521]: https://github.com/JuliaLang/julia/issues/35521
[35522]: https://github.com/JuliaLang/julia/issues/35522
[35554]: https://github.com/JuliaLang/julia/issues/35554
[35626]: https://github.com/JuliaLang/julia/issues/35626