What’s New in Go 1.18? Generics, Fuzzing, and Performance Boosts

Seven months after Go 1.17, Go 1.18 was released, bringing the language’s biggest change ever—generics—along with numerous toolchain, runtime, and library updates and performance improvements.

Generics

The most visible changes include syntax for type parameters in functions and types, instantiation using brackets, a new ~ tilde operator for type sets, expanded interface syntax allowing any type, and predeclared identifiers any (alias for interface{}) and comparable for equality‑comparable types.

Function and type declarations now accept type parameters.

Parameterized functions and types are instantiated by listing type arguments in brackets.

New ~ token added to operators and punctuation.

Interface types can embed arbitrary types and union or ~T elements, usable only as type constraints.

Predeclared identifier any is an alias for the empty interface.

Predeclared identifier comparable is an interface representing types that support == or !=, usable as a constraint.

Three experimental packages in golang.org/x/exp provide generic utilities: constraints (e.g., constraints.Ordered), slices (generic slice functions), and maps (generic map functions). These APIs are not covered by the Go 1 compatibility guarantee.

Known Limitations of the Current Generic Implementation

The compiler cannot handle type declarations inside generic functions or methods (planned for Go 1.19).

Predeclared functions real, imag, and complex cannot be used as parameter types (planned for Go 1.19).

Method sets are limited to explicitly declared methods on constraint interfaces (planned for Go 1.19).

Accessing a struct field x.f where x is a type parameter is not supported (planned for Go 1.19).

Embedding a type parameter or a pointer to one as an unnamed field in a struct or interface is disallowed.

Union elements with multiple terms may omit interface types that have non‑empty method sets.

Fuzzing

Go 1.18 includes a built‑in fuzzing implementation; see the official fuzzing tutorial to get started.

Fuzzing can consume large amounts of memory and may affect runtime performance.

The fuzz engine writes coverage data to $GOCACHE/fuzz without a limit on file count or total size, potentially using gigabytes of storage.

Compiler

The compiler can now inline functions that contain range loops or are marked as loops.

The type checker has been completely rewritten to support generics, resulting in some error messages with new wording.

Compilation speed may be about 15 % slower than Go 1.17, though execution speed is unchanged; improvements are planned for Go 1.19.

Bug fixes

Correct reporting of declared‑but‑unused variables (issue #8560).

Overflow errors are now reported when rune constants like '1' << 32 are passed to print or println.

Ports

AMD64

Go 1.18 introduces the GOAMD64 environment variable to select the minimum target version for AMD64, with allowed values v1, v2, v3, or v4 (default v1).

RISC‑V

The 64‑bit RISC‑V port on Linux now supports c-archive and c-shared build modes.

Linux

Go 1.18 requires Linux kernel 2.6.32 or newer.

Windows

Windows/arm and Windows/arm64 ports now support non‑cooperative preemption, addressing long‑standing bugs when calling Win32 functions.

iOS

The iOS simulator on iOS/arm64 and macOS/amd64 now requires iOS 12 or later; earlier versions are no longer supported.

FreeBSD

Go 1.18 is the last version to support FreeBSD 11.x; Go 1.19 requires FreeBSD 12.2+ or 13.0+.

Performance Improvements

Because Go 1.17 extended the register ABI to RM64/Apple M1/PowerPC 64, Go 1.18 delivers up to a 20 % CPU performance boost on those architectures.

For a complete list of changes, see the official release notes.

https://go.dev/dl/

https://go.dev/doc/go1.18

https://go.dev/blog/go1.18

https://go.dev/blog/tutorials-go1.18