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|
//go:build go1.21
// +build go1.21
// Package unsafe2 provides helpers to generate recursive struct types.
package unsafe2
import (
"reflect"
"unsafe"
)
type dummy struct{}
// DummyType represents a stand-in for a recursive type.
var DummyType = reflect.TypeOf(dummy{})
// The following type sizes must match their original definition in Go src/internal/abi/type.go.
type abiType struct {
_ uintptr
_ uintptr
_ uint32
_ uint8
_ uint8
_ uint8
_ uint8
_ uintptr
_ uintptr
_ int32
_ int32
}
type abiName struct {
Bytes *byte
}
type abiStructField struct {
Name abiName
Typ *abiType
Offset uintptr
}
type abiStructType struct {
abiType
PkgPath abiName
Fields []abiStructField
}
type emptyInterface struct {
typ *abiType
_ unsafe.Pointer
}
// SetFieldType sets the type of the struct field at the given index, to the given type.
//
// The struct type must have been created at runtime. This is very unsafe.
func SetFieldType(s reflect.Type, idx int, t reflect.Type) {
if s.Kind() != reflect.Struct || idx >= s.NumField() {
return
}
rtyp := unpackType(s)
styp := (*abiStructType)(unsafe.Pointer(rtyp))
f := styp.Fields[idx]
f.Typ = unpackType(t)
styp.Fields[idx] = f
}
func unpackType(t reflect.Type) *abiType {
v := reflect.New(t).Elem().Interface()
eface := *(*emptyInterface)(unsafe.Pointer(&v))
return eface.typ
}
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