Julia v1.10 Release Notes
========================

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

* JuliaSyntax.jl is now used as the default parser, providing better diagnostics and faster
  parsing. Set environment variable `JULIA_USE_NEW_PARSER` to `0` to switch back to the old
  parser if necessary (and if you find this necessary, please file an issue) ([#46372]).
* `⥺` (U+297A, `\leftarrowsubset`) and `⥷` (U+2977, `\leftarrowless`)
  may now be used as binary operators with arrow precedence. ([#45962])

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

* When a task forks a child, the parent task's task-local RNG (random number generator) is no longer affected. The seeding of child based on the parent task also takes a more disciplined approach to collision resistance, using a design based on the SplitMix and DotMix splittable RNG schemes ([#49110]).
* A new more-specific rule for methods resolves ambiguities containing Union{} in favor of
  the method defined explicitly to handle the Union{} argument. This makes it possible to
  define methods to explicitly handle Union{} without the ambiguities that commonly would
  result previously. This also lets the runtime optimize certain method lookups in a way
  that significantly improves load and inference times for heavily overloaded methods that
  dispatch on Types (such as traits and constructors).
* The "h bar" `ℏ` (`\hslash` U+210F) character is now treated as equivalent to `ħ` (`\hbar` U+0127).
* The `@simd` macro now has a more limited and clearer semantics, it only enables reordering and contraction
  of floating-point operations, instead of turning on all "fastmath" optimizations.
  If you observe performance regressions due to this change, you can recover previous behavior with `@fastmath @simd`,
  if you are OK with all the optimizations enabled by the `@fastmath` macro. ([#49405])
* When a method with keyword arguments is displayed in the stack trace view, the textual
  representation of the keyword arguments' types is simplified using the new
  `@Kwargs{key1::Type1, ...}` macro syntax ([#49959]).

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

* The `@pure` macro is now deprecated. Use `Base.@assume_effects :foldable` instead ([#48682]).
* The mark phase of the Garbage Collector is now multi-threaded ([#48600]).
* [JITLink](https://llvm.org/docs/JITLink.html) is enabled by default on Linux aarch64 when Julia is linked to LLVM 15 or later versions ([#49745]).
  This should resolve many segmentation faults previously observed on this platform.

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

* New option `--gcthreads` to set how many threads will be used by the Garbage Collector ([#48600]).
  The default is set to `N/2` where `N` is the amount of worker threads (`--threads`) used by Julia.

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


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


New library functions
---------------------
* `tanpi` is now defined. It computes tan(πx) more accurately than `tan(pi*x)` ([#48575]).
* `fourthroot(x)` is now defined in `Base.Math` and can be used to compute the fourth root of `x`.
   It can also be accessed using the unicode character `∜`, which can be typed by `\fourthroot<tab>` ([#48899]).
* `Libc.memmove`, `Libc.memset`, and `Libc.memcpy` are now defined, whose functionality matches that of their respective C calls.
* `Base.isprecompiled(pkg::PkgId)` to identify whether a package has already been precompiled ([#50218]).

New library features
--------------------
* The `initialized=true` keyword assignment for `sortperm!` and `partialsortperm!`
  is now a no-op ([#47979]). It previously exposed unsafe behavior ([#47977]).
* `binomial(x, k)` now supports non-integer `x` ([#48124]).
* A `CartesianIndex` is now treated as a "scalar" for broadcasting ([#47044]).
* `printstyled` now supports italic output ([#45164]).
* `parent` and `parentindices` support `SubString`s

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

* `startswith` now supports seekable `IO` streams ([#43055])
* printing integral `Rational`s will skip the denominator in `Rational`-typed IO context (e.g. in `Arrays`) ([#45396])

#### Package Manager

* `Pkg.precompile` now accepts `timing` as a keyword argument which displays per package timing information for precompilation (e.g. `Pkg.precompile(timing=true)`)

#### LinearAlgebra

* `AbstractQ` no longer subtypes to `AbstractMatrix`. Moreover, `adjoint(Q::AbstractQ)`
  no longer wraps `Q` in an `Adjoint` type, but instead in an `AdjointQ`, that itself
  subtypes `AbstractQ`. This change accounts for the fact that typically `AbstractQ`
  instances behave like function-based, matrix-backed linear operators, and hence don't
  allow for efficient indexing. Also, many `AbstractQ` types can act on vectors/matrices
  of different size, acting like a matrix with context-dependent size. With this change,
  `AbstractQ` has a well-defined API that is described in detail in the
  [Julia documentation](https://docs.julialang.org/en/v1/stdlib/LinearAlgebra/#man-linalg-abstractq)
  ([#46196]).
* Adjoints and transposes of `Factorization` objects are no longer wrapped in `Adjoint`
  and `Transpose` wrappers, respectively. Instead, they are wrapped in
  `AdjointFactorization` and `TranposeFactorization` types, which themselves subtype
  `Factorization` ([#46874]).
* New functions `hermitianpart` and `hermitianpart!` for extracting the Hermitian
  (real symmetric) part of a matrix ([#31836]).
* The `norm` of the adjoint or transpose of an `AbstractMatrix` now returns the norm of the
  parent matrix by default, matching the current behaviour for `AbstractVector`s ([#49020]).
* `eigen(A, B)` and `eigvals(A, B)`, where one of `A` or `B` is symmetric or Hermitian,
  are now fully supported ([#49533])
* `eigvals/eigen(A, cholesky(B))` now computes the generalized eigenvalues (`eigen`: and eigenvectors)
  of `A` and `B` via Cholesky decomposition for positive definite `B`. Note: The second argument is
  the output of `cholesky`.

#### Printf
* Format specifiers now support dynamic width and precision, e.g. `%*s` and `%*.*g` ([#40105]).

#### Profile


#### Random


#### REPL

* When stack traces are printed, the printed depth of types in function signatures will be limited
  to avoid overly verbose output ([#49795]).

#### SuiteSparse


#### SparseArrays


#### Test


* The `@test_broken` macro (or `@test` with `broken=true`) now complains if the test expression returns a
  non-boolean value in the same way as a non-broken test. ([#47804])
* When a call to `@test` fails or errors inside a function, a larger stacktrace is now printed such that the location of the test within a `@testset` can be retrieved ([#49451])

#### Dates


#### Distributed


#### Unicode


#### DelimitedFiles


#### InteractiveUtils

 * `code_native` and `@code_native` now default to intel syntax instead of AT&T.
 * `@time_imports` now shows the timing of any module `__init__()`s that are run ([#49529])

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


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


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


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