https://go.dev/blog/go1.21rc

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The Go Blog

Go 1.21 Release Candidate

Eli Bendersky, on behalf of the Go team
21 June 2023

The Go 1.21 first Release Candidate (RC) is available today on the
download page! Go 1.21 is packed with new features and improvements.
Getting the RC (release candidate) allows you to experiment with it
early, try it on your workloads, and report any issues before the
final release (scheduled for August). Here are some notable changes
and features in Go 1.21; for the full list, refer to the full release
notes.

(Please note that the first RC for Go 1.21 is called go1.21rc2
because a bug was found and fixed after tagging go1.21rc1)

Tool improvements

  * The Profile Guided Optimization (PGO) feature we announced for
    preview in 1.20 is now generally available! If a file named
    default.pgo is present in the main package's directory, the go
    command will use it to enable a PGO build. See the PGO
    documentation for more details. We've measured the impact of PGO
    on a wide set of Go programs and see performance improvements of
    2-7%.
  * The go tool now supports backward and forward language
    compatibility.

Language changes

  * New built-in functions: min, max and clear.
  * Several improvements to type inference for generic functions. The
    description of type inference in the spec has been expanded and
    clarified.
  * In a future version of Go we're planning to address one of the
    most common gotchas of Go programming: loop variable capture. Go
    1.21 comes with a preview of this feature that you can enable in
    your code using an environment variable. See this
    LoopvarExperiment wiki page for more details.

Standard library additions

  * New log/slog package for structured logging.
  * New slices package for common operations on slices of any element
    type. This includes sorting functions that are generally faster
    and more ergonomic than the sort package.
  * New maps package for common operations on maps of any key or
    element type.
  * New cmp package with new utilities for comparing ordered values.

Improved performance

In addition to the performance improvements when enabling PGO:

  * The Go compiler itself has been rebuilt with PGO enabled for
    1.21, and as a result it builds Go programs 2-4% faster,
    depending on the host architecture.
  * Due to tuning of the garbage collector, some applications may see
    up to a 40% reduction in tail latency.
  * Collecting traces with runtime/trace now incurs a substantially
    smaller CPU cost on amd64 and arm64.

A new port to WASI

Go 1.21 adds an experimental port for WebAssembly System Interface
(WASI), Preview 1 (GOOS=wasip1, GOARCH=wasm).

To facilitate writing more general WebAssembly (WASM) code, the
compiler also supports a new directive for importing functions from
the WASM host: go:wasmimport.

Please download the Go 1.21 RC and try it! If you notice any
problems, please file an issue.

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