Go 1.23+ Knowledge Patch Skill

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)
}

Agent Skills: Go 1.23+ Knowledge Patch

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