Golang Type.At方法代码示例

// flatten returns a list of directly contained fields in the preorder
// traversal of the type tree of t.  The resulting elements are all
// scalars (basic types or pointerlike types), except for struct/array
// "identity" nodes, whose type is that of the aggregate.
//
// reflect.Value is considered pointerlike, similar to interface{}.
//
// Callers must not mutate the result.
//
func (a *analysis) flatten(t types.Type) []*fieldInfo {
	fl, ok := a.flattenMemo[t]
	if !ok {
		switch t := t.(type) {
		case *types.Named:
			u := t.Underlying()
			if isInterface(u) {
				// Debuggability hack: don't remove
				// the named type from interfaces as
				// they're very verbose.
				fl = append(fl, &fieldInfo{typ: t})
			} else {
				fl = a.flatten(u)
			}

		case *types.Basic,
			*types.Signature,
			*types.Chan,
			*types.Map,
			*types.Interface,
			*types.Slice,
			*types.Pointer:
			fl = append(fl, &fieldInfo{typ: t})

		case *types.Array:
			fl = append(fl, &fieldInfo{typ: t}) // identity node
			for _, fi := range a.flatten(t.Elem()) {
				fl = append(fl, &fieldInfo{typ: fi.typ, op: true, tail: fi})
			}

		case *types.Struct:
			fl = append(fl, &fieldInfo{typ: t}) // identity node
			for i, n := 0, t.NumFields(); i < n; i++ {
				f := t.Field(i)
				for _, fi := range a.flatten(f.Type()) {
					fl = append(fl, &fieldInfo{typ: fi.typ, op: f, tail: fi})
				}
			}

		case *types.Tuple:
			// No identity node: tuples are never address-taken.
			n := t.Len()
			if n == 1 {
				// Don't add a fieldInfo link for singletons,
				// e.g. in params/results.
				fl = append(fl, a.flatten(t.At(0).Type())...)
			} else {
				for i := 0; i < n; i++ {
					f := t.At(i)
					for _, fi := range a.flatten(f.Type()) {
						fl = append(fl, &fieldInfo{typ: fi.typ, op: i, tail: fi})
					}
				}
			}

		default:
			panic(t)
		}

		a.flattenMemo[t] = fl
	}

	return fl
}

// zero returns a new "zero" value of the specified type.
func zero(t types.Type) value {
	switch t := t.(type) {
	case *types.Basic:
		if t.Kind() == types.UntypedNil {
			panic("untyped nil has no zero value")
		}
		if t.Info()&types.IsUntyped != 0 {
			// TODO(adonovan): make it an invariant that
			// this is unreachable.  Currently some
			// constants have 'untyped' types when they
			// should be defaulted by the typechecker.
			t = ssa.DefaultType(t).(*types.Basic)
		}
		switch t.Kind() {
		case types.Bool:
			return false
		case types.Int:
			return int(0)
		case types.Int8:
			return int8(0)
		case types.Int16:
			return int16(0)
		case types.Int32:
			return int32(0)
		case types.Int64:
			return int64(0)
		case types.Uint:
			return uint(0)
		case types.Uint8:
			return uint8(0)
		case types.Uint16:
			return uint16(0)
		case types.Uint32:
			return uint32(0)
		case types.Uint64:
			return uint64(0)
		case types.Uintptr:
			return uintptr(0)
		case types.Float32:
			return float32(0)
		case types.Float64:
			return float64(0)
		case types.Complex64:
			return complex64(0)
		case types.Complex128:
			return complex128(0)
		case types.String:
			return ""
		case types.UnsafePointer:
			return unsafe.Pointer(nil)
		default:
			panic(fmt.Sprint("zero for unexpected type:", t))
		}
	case *types.Pointer:
		return (*value)(nil)
	case *types.Array:
		a := make(array, t.Len())
		for i := range a {
			a[i] = zero(t.Elem())
		}
		return a
	case *types.Named:
		return zero(t.Underlying())
	case *types.Interface:
		return iface{} // nil type, methodset and value
	case *types.Slice:
		return []value(nil)
	case *types.Struct:
		s := make(structure, t.NumFields())
		for i := range s {
			s[i] = zero(t.Field(i).Type())
		}
		return s
	case *types.Tuple:
		if t.Len() == 1 {
			return zero(t.At(0).Type())
		}
		s := make(tuple, t.Len())
		for i := range s {
			s[i] = zero(t.At(i).Type())
		}
		return s
	case *types.Chan:
		return chan value(nil)
	case *types.Map:
		if usesBuiltinMap(t.Key()) {
			return map[value]value(nil)
		}
		return (*hashmap)(nil)
	case *types.Signature:
		return (*ssa.Function)(nil)
	}
	panic(fmt.Sprint("zero: unexpected ", t))
}