Julia v1.13 Release Notes

New language features

New Base.@acquire macro for a non-closure version of Base.acquire(f, s::Base.Semaphore), like @lock. (#56845)
New nth function to access the n-th element of a generic iterable. (#56580)
New @__FUNCTION__ macro to refer to the innermost enclosing function. (#58940)
The character U+1F8B2 🢲 (RIGHTWARDS ARROW WITH LOWER HOOK), newly added by Unicode 16, is now a valid operator with arrow precedence, accessible as \hookunderrightarrow at the REPL. ([JuliaLang/JuliaSyntax.jl#525], #57143)

mod(x::AbstractFloat, -Inf) now returns x (as long as x is finite), this aligns with C standard and

is considered a bug fix (#47102)

The hash algorithm and its values have changed. Most hash specializations will remain correct and require no action. Types that reimplement the core hashing logic independently, such as some third-party string packages do, may require a migration to the new algorithm. (#57509)
Indexless getindex and setindex! (i.e. A[]) on ReinterpretArray now correctly throw a BoundsError when there is more than one element. (#58814)

The option --sysimage-native-code=no has been deprecated.
The JULIA_CPU_TARGET environment variable now supports a sysimage keyword to match (or extend) the CPU target used to build the current system image (#58970).

A new AbstractSpinLock is defined with SpinLock <: AbstractSpinLock (#55944).
A new PaddedSpinLock <: AbstractSpinLock is defined. It has extra padding to avoid false sharing (#55944).
New types are defined to handle the pattern of code that must run once per process, called a OncePerProcess{T} type, which allows defining a function that should be run exactly once the first time it is called, and then always return the same result value of type T every subsequent time afterwards. There are also OncePerThread{T} and OncePerTask{T} types for similar usage with threads or tasks. ([#TBD])

ispositive(::Real) and isnegative(::Real) are provided for performance and convenience (#53677).
Exporting function fieldindex to get the index of a struct's field (#58119).
Base.donotdelete is now public. It prevents deadcode elemination of its arguments (#55774).
Sys.sysimage_target() returns the CPU target string used to build the current system image (#58970).

fieldoffset now also accepts the field name as a symbol as fieldtype already did (#58100).
sort(keys(::Dict)) and sort(values(::Dict)) now automatically collect, they previously threw (#56978).
Base.AbstractOneTo is added as a supertype of one-based axes, with Base.OneTo as its subtype (#56902).
takestring!(::IOBuffer) removes the content from the buffer, returning the content as a String.

randperm! and randcycle! now support non-Array AbstractArray inputs, assuming they are mutable and their indices are one-based (#58596).

The display of AbstractChars in the main REPL mode now includes LaTeX input information like what is shown in help mode (#58181).
Display of repeated frames and cycles in stack traces has been improved by bracketing them in the trace and treating them consistently (#55841).

Test failures when using the @test macro now show evaluated arguments for all function calls (#57825, #57839).
Transparent test sets (@testset let) now show context when tests error (#58727).
@test_throws now supports a three-argument form @test_throws ExceptionType pattern expr to test both exception type and message pattern in one call (#59117).

Introspection utilities such as @code_typed, @which and @edit now accept type annotations as substitutes for values, recognizing forms such as f(1, ::Float64, 3) or even sum(::Vector{T}; init = ::T) where {T<:Real}. Type-annotated variables as in f(val::Int; kw::Float64) are not evaluated if the type annotation provides the necessary information, making this syntax compatible with signatures found in stacktraces (#57909, #58222).
Code introspection macros such as @code_lowered and @code_typed now have a much better support for broadcasting expressions, including broadcasting assignments of the form x .+= f(y) (#58349).