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_FLISP_PARSER to 1 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). (#49349)
  • The "h bar" (\hslash U+210F) character is now treated as equivalent to ħ (\hbar U+0127).
  • The @simd macro now has 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' type is simplified using the new @Kwargs{key1::Type1, ...} macro syntax (#49959).

Compiler/Runtime improvements

  • The mark phase of the garbage collector is now multi-threaded (#48600).
  • JITLink 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.
  • The precompilation process now uses pidfile locks and orchestrates multiple julia processes to only have one process spend effort precompiling while the others wait. Previously all would do the work and race to overwrite the cache files. (#49052)

Command-line option changes

  • New option --gcthreads to set how many threads will be used by the garbage collector (#48600). The default is N/2 where N is the number of worker threads (--threads) used by Julia.

Build system changes

  • SparseArrays and SuiteSparse are no longer included in the default system image, so the core language no longer contains GPL libraries. However, these libraries are still included alongside the language in the standard binary distribution (#44247, #48979, #49266).

New library functions

  • tanpi is now defined. It computes tan(πx) more accurately than `tan(pix)` (#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) has been added, to identify whether a package has already been precompiled (#50218).

New library features

  • 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 SubStrings.
  • replace(string, pattern...) now supports an optional IO argument to write the output to a stream rather than returning a string (#48625).
  • startswith now supports seekable IO streams (#43055).

Standard library changes

  • The initialized=true keyword assignment for sortperm! and partialsortperm! is now a no-op (#47979). It previously exposed unsafe behavior (#47977).
  • Printing integral Rationals 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)).


  • AbstractQ no longer subtypes 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 (#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 AbstractVectors (#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.


  • Format specifiers now support dynamic width and precision, e.g. %*s and %*.*g (#40105).


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


  • 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).


  • 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

  • The @pure macro is now deprecated. Use Base.@assume_effects :foldable instead (#48682).