Go 1.21, the latest update of Google’s Go programming language, is now available as a release candidate. The new version adds built-in functions—min, max, and clear—and makes profile-guided optimization (PGO) generally available. WebAssembly accommodations also are highlighted.

The min and max functions compute the smallest or largest value, respectively, of a fixed number of arguments or ordered types. There must be at least one argument. The clear function takes an argument of map, slice, or type parameter type and deletes or zeroes out all of the elements.

Published June 21, the Go 1.21 release candidate can be downloaded from the project website, with the release labeled as RC2 due to a bug having been found and fixed after go1.21.rc1. The production release is expected in August.

Profile-guided optimization, introduced as a preview in Go 1.20 in February, graduates from preview status in the new version. PGO enables the compiler toolchain to do workload-specific and application-specific optimizations based on runtime profile information. So far, PGO has improved performance by 2% to 7% when the impact was measured on a wide set of programs, Go project developers said. The Go compiler has been rebuilt with PGO enabled.

Go 1.21 promises additional performance improvements. Tuning the garbage collector could result in some applications seeing as much as a 40% reduction in tail latency, while collecting traces with runtime/trace now incurs a much smaller CPU cost on AMD64 and Arm64 systems.

Elsewhere in Go 1.21:

• An experimental WASI (WebAssembly System Interface) port is being previewed. To help with writing more general WebAssembly code, the compiler also supports a new wasmimport directive for importing functions from the Wasm host. 
• The standard library adds a new log/slog package for structured logging. A new slices package is offered for common operations on slices of any element types. This includes sorting functions that are generally faster and more ergonomic than the sort package.
• The standard library also adds a new maps package for common operations on maps of any key or element type. A new cmp package includes new utilities for comparing ordered values.
• The go tool now supports both backward and forward language compatibility.
• Improvements have been made to type inference for generic functions. The description of type inference has been expanded and clarified in the spec.
• A future version of Go will address a common “gotcha” with the language: loop variable capture. Go 1.21 previews this capability, which can be enabled in code using an environment variable.