Julia v1.15 Release Notes

New language features

Language changes

Slices exposes dataids of its parent array to properly identify aliasing in broadcasting (#49182).

Compiler/Runtime improvements

After a sweep, Julia's default garbage collector now lets any thread reuse the free cells of pages that still hold live objects, instead of only the thread that allocated the page. This reduces the memory footprint of workloads that allocate many small objects on many threads and keep few of them, such as a language server that runs type inference repeatedly (#63512).

Command-line option changes

--code-coverage=-<paths> records no coverage for files under the given paths, and optimizes their code as if coverage were off, so that instrumenting a test suite does not change how its own functions are compiled.
--code-coverage=@<paths> and --track-allocation=@<paths> accept a list of paths (#54698).

Multi-threading changes

--threads=auto, --procs=auto, JULIA_NUM_THREADS=auto and the default number of GC threads now honour JULIA_CPU_THREADS, matching Sys.EFFECTIVE_CPU_THREADS (#64613).
With JULIA_EXCLUSIVE=1, default-pool threads are pinned to the CPUs of the inherited affinity mask, in order, instead of to CPUs 0 to N-1. Their number is limited by that mask rather than by Sys.EFFECTIVE_CPU_THREADS (#64613).

Build system changes

base/userimg.jl is no longer supported, and the build now fails if it exists. To build a system image with additional code, use PackageCompiler.jl, or run a script on top of an existing system image with julia --sysimage <image> --output-o <file> <script>.

New library functions

bitsizeof(x) returns the declared width in bits of a primitive type, or of the primitive type of x, excluding the padding that sizeof includes. It throws for any other type or value (#61359).
filterfirst(f, itr) returns the first element of itr for which f returns true (#60913).
growat!(a::Vector, i, delta) grows a by delta uninitialized elements inserted at index i (#63573).

New library features

Standard library changes

Dates

InteractiveUtils

JuliaSyntaxHighlighting

Libdl

LinearAlgebra

Markdown

Mmap

Profile

Random

REPL

SharedArrays

Sockets

Test

TOML

UUIDs

uuid5 now hashes the bytes of name as specified by RFC 4122, instead of first processing backslash escape sequences in it with unescape_string. This changes the result for names containing a backslash, which previously could also throw an ArgumentError.

External dependencies

Tooling Improvements

Deprecated or removed