Go 1.23+ Knowledge Patch

Claude's baseline knowledge covers Go through 1.22. This skill provides features from 1.23 (2024) onwards.

Quick Reference

Language Changes (1.26)

Feature	Syntax
Pointer from expression	new(42), new(yearsSince(born))
Self-referential generics	type Adder[A Adder[A]] interface { Add(A) A }

See references/language-changes.md for details and migration patterns.

Standard Library (1.26)

Package	Addition	Purpose
errors	AsType[T](err)	Generic type-safe error matching
bytes	Buffer.Peek(n)	Read next n bytes without advancing
log/slog	NewMultiHandler(h...)	Fan out to multiple log handlers
reflect	Type.Fields(), .Methods(), .Ins(), .Outs()	Iterator methods on types
reflect	Value.Fields(), .Methods()	Iterator methods yielding type+value
testing	T.ArtifactDir()	Directory for test output artifacts

See references/stdlib-updates.md for full API details and examples.

Tooling (1.26)

Command	Purpose
go fix ./...	Rewritten modernizer — updates code to current idioms
//go:fix inline	Directive for custom API migration rules

See references/tooling.md for modernizer details.

Reference Files

File	Contents
language-changes.md	new(expr), self-referential generic constraints
stdlib-updates.md	errors.AsType, bytes.Buffer.Peek, slog.NewMultiHandler, reflect iterators, testing artifacts
tooling.md	go fix modernizers, //go:fix inline directive

Critical Knowledge

new(expr) Replaces ptr() Helpers (1.26)

The most common impact — eliminates the ubiquitous ptr[T any](v T) *T helper:

// Before: needed a helper or temp variable
func ptr[T any](v T) *T { return &v }
p := ptr(42)

// After: built-in
p := new(42)
p := new(yearsSince(born)) // useful for optional struct fields

errors.AsType — No More Temp Variables (1.26)

// Before
var pathErr *fs.PathError
if errors.As(err, &pathErr) {
	use(pathErr)
}

// After — no separate variable needed
if pe, ok := errors.AsType[*fs.PathError](err); ok {
	use(pe)
}

Reflect Iterators (1.26)

Range over struct fields, method sets, and function signatures:

for sf, v := range reflect.ValueOf(s).Fields() {
	fmt.Println(sf.Name, v)
}