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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/reflect/type.go.
type rtype struct {
_ uintptr
_ uintptr
_ uint32
_ uint32
_ uintptr
_ uintptr
_ uint32
_ uint32
}
type emptyInterface struct {
typ *rtype
_ unsafe.Pointer
}
type structField struct {
_ uintptr
typ *rtype
_ uintptr
}
type structType struct {
rtype
_ uintptr
fields []structField
}
// 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 := (*structType)(unsafe.Pointer(rtyp))
f := styp.fields[idx]
f.typ = unpackType(t)
styp.fields[idx] = f
}
func unpackType(t reflect.Type) *rtype {
v := reflect.New(t).Elem().Interface()
return (*emptyInterface)(unsafe.Pointer(&v)).typ
}
|
