# Julia v1.8 Release Notes

## New language features

- Mutable struct fields may now be annotated as `const` to prevent changing them after construction, providing for greater clarity and optimization ability of these objects (#43305).
- Type annotations can now be added to global variables to make accessing them type stable (#43671).
- Empty n-dimensional arrays can now be created using multiple semicolons inside square brackets, e.g. `[;;;]` creates a 0×0×0 `Array` (#41618).
- `try`-blocks can now optionally have an `else`-block which is executed right after the main body only if no errors were thrown (#42211).
- `@inline` and `@noinline` annotations can now be placed within a function body (#41312).
- `@inline` and `@noinline` annotations can now be applied to a function call site or block to enforce the involved function calls to be (or not to be) inlined (#41312).
- `∀`, `∃`, and `∄` are now allowed as identifier characters (#42314).
- Support for Unicode 14.0.0 (#43443).
- `Module(:name, false, false)` can be used to create a `module` that contains no names (it does not import `Base` or `Core` and does not contain a reference to itself) ([#40110, #42154]).

## Language changes

- Newly-created Task objects (`@spawn`, `@async`, etc.) now adopt the world age for methods from their parent Task upon creation, instead of using the global latest world at start. This is done to enable inference to eventually optimize these calls. Places that wish for the old behavior may use `Base.invokelatest` (#41449).
- Unbalanced Unicode bidirectional formatting directives are now disallowed within strings and comments, to mitigate the "trojan source" vulnerability (#42918).
- `Base.ifelse` is now defined as a generic function rather than a builtin one, allowing packages to extend its definition (#37343).
- Every assignment to a global variable now first goes through a call to `convert(Any, x)` (or `convert(T, x)` respectively if a type `T` has been declared for the global). This means great care should be taken to ensure the invariant `convert(Any, x) === x` always holds, as this change could otherwise lead to unexpected behavior (#43671).
- Builtin functions are now a bit more like generic functions, and can be enumerated with `methods` (#43865).

## Compiler/Runtime improvements

- Bootstrapping time has been improved by about 25% (#41794).
- The LLVM-based compiler has been separated from the run-time library into a new library, `libjulia-codegen`. It is loaded by default, so normal usage should see no changes. In deployments that do not need the compiler (e.g. system images where all needed code is precompiled), this library (and its LLVM dependency) can simply be excluded (#41936).
- Conditional type constraints can now be forwarded interprocedurally (i.e. propagated from caller to callee) (#42529).
- Julia-level SROA (Scalar Replacement of Aggregates) has been improved: allowing elimination of `getfield` calls with constant global fields (#42355), enabling elimination of mutable structs with uninitialized fields (#43208), improving performance (#43232), and handling more nested `getfield` calls (#43239).
- Abstract call sites can now be inlined or statically resolved as long as the call site has a single matching method (#43113).
- Inference now tracks various effects such as side-effectful-ness and nothrow-ness on a per-specialization basis. Code heavily dependent on constant propagation should see significant compile-time performance improvements and certain cases (e.g. calls to uninlinable functions that are nevertheless effect free) should see runtime performance improvements. Effects may be overwritten manually with the `@Base.assume_effects` macro (#43852).

## Command-line option changes

- The default behavior of observing `@inbounds` declarations is now an option via `auto` in `--check-bounds=yes|no|auto` (#41551).
- New option `--strip-metadata` to remove docstrings, source location information, and local variable names when building a system image (#42513).
- New option `--strip-ir` to remove the compiler's IR (intermediate representation) of source code when building a system image. The resulting image will only work if `--compile=all` is used, or if all needed code is precompiled (#42925).
- When the program file is `-` the code to be executed is read from standard in (#43191).

## Multi-threading changes

- `Threads.@threads` now defaults to a new `:dynamic` schedule option which is similar to the previous behavior except that iterations will be scheduled dynamically to available worker threads rather than pinned to each thread. This behavior is more composable with (possibly nested) `@spawn` and `@threads` loops (#43919, #44136).

## Build system changes

## New library functions

- New function `eachsplit(str)` for iteratively performing `split(str)` (#39245).
- New function `allequal(itr)` for testing if all elements in an iterator are equal (#43354).
- `hardlink(src, dst)` can be used to create hard links (#41639).
- `setcpuaffinity(cmd, cpus)` can be used to set CPU affinity of sub-processes (#42469).
- `diskstat(path=pwd())` can be used to return statistics about the disk (#42248).
- New `@showtime` macro to show both the line being evaluated and the `@time` report (#42431).
- The `LazyString` and the `lazy"str"` macro were added to support delayed construction of error messages in error paths (#33711).

## New library features

- `@time` and `@timev` now take an optional description to allow annotating the source of time reports, e.g. `@time "Evaluating foo" foo()` (#42431).
- `range` accepts either `stop` or `length` as a sole keyword argument (#39241).
- `precision` and `setprecision` now accept a `base` keyword argument (#42428).
- TCP socket objects now expose `closewrite` functionality and support half-open mode usage (#40783).
- `extrema` now accepts an `init` keyword argument (#36265, #43604).
- `Iterators.countfrom` now accepts any type that defines `+` (#37747).

## Standard library changes

- Keys with value `nothing` are now removed from the environment in `addenv` (#43271).
- `Iterators.reverse` (and hence `last`) now supports `eachline` iterators (#42225).
- The `length` function on certain ranges of certain element types no longer checks for integer overflow in most cases. The new function `checked_length` is now available, which will try to use checked arithmetic to error if the result may be wrapping. Or use a package such as SaferIntegers.jl when constructing the range (#40382).
- Intersect returns a result with the eltype of the type-promoted eltypes of the two inputs (#41769).
- Iterating an `Iterators.Reverse` now falls back on reversing the eachindex iterator, if possible (#43110).

#### InteractiveUtils

- New macro `@time_imports` for reporting any time spent importing packages and their dependencies (#41612).

#### LinearAlgebra

- The BLAS submodule now supports the level-2 BLAS subroutine `spr!` (#42830).
- `cholesky[!]` now supports `LinearAlgebra.PivotingStrategy` (singleton type) values as its optional `pivot` argument: the default is `cholesky(A, NoPivot())` (vs. `cholesky(A, RowMaximum())`); the former `Val{true/false}`-based calls are deprecated (#41640).
- The standard library `LinearAlgebra.jl` is now completely independent of `SparseArrays.jl`, both in terms of the source code as well as unit testing (#43127). As a consequence, sparse arrays are no longer (silently) returned by methods from `LinearAlgebra` applied to `Base` or `LinearAlgebra` objects. Specifically, this results in the following breaking changes:
  - Concatenations involving special "sparse" matrices (`*diagonal`) now return dense matrices; As a consequence, the `D1` and `D2` fields of `SVD` objects, constructed upon `getproperty` calls are now dense matrices.
  - 3-arg `similar(::SpecialSparseMatrix, ::Type, ::Dims)` returns a dense zero matrix. As a consequence, products of bi-, tri- and symmetric tridiagonal matrices with each other result in dense output. Moreover, constructing 3-arg similar matrices of special "sparse" matrices of (nonstatic) matrices now fails for the lack of `zero(::Type{Matrix{T}})`.

#### Printf

- Now uses `textwidth` for formatting `%s` and `%c` widths (#41085).

#### Profile

- CPU profiling now records sample metadata including thread and task. `Profile.print()` has a new `groupby` kwarg that allows grouping by thread, task, or nested thread/task, task/thread, and `threads` and `tasks` kwargs to allow filtering. Further, percent utilization is now reported as a total or per-thread, based on whether the thread is idle or not at each sample. `Profile.fetch()` includes the new metadata by default. For backwards compatibility with external profiling data consumers, it can be excluded by passing `include_meta=false` (#41742).
- The new `Profile.Allocs` module allows memory allocations to be profiled. The stack trace, type, and size of each allocation is recorded, and a `sample_rate` argument allows a tunable amount of allocations to be skipped, reducing performance overhead (#42768).
- A fixed duration cpu profile can now be triggered by the user during running tasks without `Profile` being loaded first and the report will show during execution. On MacOS & FreeBSD press `ctrl-t` or raise a `SIGINFO`. For other platforms raise a `SIGUSR1` i.e. `% kill -USR1 $julia_pid`. Not currently available on windows (#43179).

#### REPL

- `RadioMenu` now supports optional `keybindings` to directly select options (#41576).
- `?(x, y` followed by TAB displays all methods that can be called with arguments `x, y, ...`. (The space at the beginning prevents entering help-mode.) `MyModule.?(x, y` limits the search to `MyModule`. TAB requires that at least one argument have a type more specific than `Any`; use SHIFT-TAB instead of TAB to allow any compatible methods (#38791).
- New `err` global variable in `Main` set when an expression throws an exception, akin to `ans`. Typing `err` reprints the exception information (#40642).

#### SparseArrays

- The code for SparseArrays has been moved from the Julia repo to the external repo at https://github.com/JuliaSparse/SparseArrays.jl. This is only a code movement and does not impact any usage (#43813).
- New sparse concatenation functions `sparse_hcat`, `sparse_vcat`, and `sparse_hvcat` return `SparseMatrixCSC` output independent from the types of the input arguments. They make concatenation behavior available, in which the presence of some special "sparse" matrix argument resulted in sparse output by multiple dispatch. This is no longer possible after making `LinearAlgebra.jl` independent from `SparseArrays.jl` (#43127).

#### Logging

- The standard log levels `BelowMinLevel`, `Debug`, `Info`, `Warn`, `Error`, and `AboveMaxLevel` are now exported from the Logging stdlib (#40980).

#### Unicode

- Added function `isequal_normalized` to check for Unicode equivalence without explicitly constructing normalized strings (#42493).
- The `Unicode.normalize` function now accepts a `chartransform` keyword that can be used to supply custom character mappings, and a `Unicode.julia_chartransform` function is provided to reproduce the mapping used in identifier normalization by the Julia parser (#42561).

#### Test

- `@test_throws "some message" triggers_error()` can now be used to check whether the displayed error text contains "some message" regardless of the specific exception type. Regular expressions, lists of strings, and matching functions are also supported (#41888).
- `@testset foo()` can now be used to create a test set from a given function. The name of the test set is the name of the called function. The called function can contain `@test` and other `@testset` definitions, including to other function calls, while recording all intermediate test results (#42518).
- `TestLogger` and `LogRecord` are now exported from the Test stdlib (#44080).

## Deprecated or removed

## External dependencies

## Tooling Improvements

- `GC.enable_logging(true)` can be used to log each garbage collection, with the time it took and the amount of memory that was collected (#43511).

Theme

This document was generated with Documenter.jl version 0.27.12 on Friday 25 February 2022. Using Julia version 1.8.0-beta1.