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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements commonly used type predicates.
package types
import "sort"
func isNamed(typ Type) bool {
if _, ok := typ.(*Basic); ok {
return ok
}
_, ok := typ.(*Named)
return ok
}
func isBoolean(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsBoolean != 0
}
func isInteger(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsInteger != 0
}
func isUnsigned(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsUnsigned != 0
}
func isFloat(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsFloat != 0
}
func isComplex(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsComplex != 0
}
func isNumeric(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsNumeric != 0
}
func isString(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsString != 0
}
func isTyped(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return !ok || t.info&IsUntyped == 0
}
func isUntyped(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsUntyped != 0
}
func isOrdered(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsOrdered != 0
}
func isConstType(typ Type) bool {
t, ok := typ.Underlying().(*Basic)
return ok && t.info&IsConstType != 0
}
// IsInterface reports whether typ is an interface type.
func IsInterface(typ Type) bool {
_, ok := typ.Underlying().(*Interface)
return ok
}
// Comparable reports whether values of type T are comparable.
func Comparable(T Type) bool {
switch t := T.Underlying().(type) {
case *Basic:
// assume invalid types to be comparable
// to avoid follow-up errors
return t.kind != UntypedNil
case *Pointer, *Interface, *Chan:
return true
case *Struct:
for _, f := range t.fields {
if !Comparable(f.typ) {
return false
}
}
return true
case *Array:
return Comparable(t.elem)
}
return false
}
// hasNil reports whether a type includes the nil value.
func hasNil(typ Type) bool {
switch t := typ.Underlying().(type) {
case *Basic:
return t.kind == UnsafePointer
case *Slice, *Pointer, *Signature, *Interface, *Map, *Chan:
return true
}
return false
}
// Identical reports whether x and y are identical types.
// Receivers of Signature types are ignored.
func Identical(x, y Type) bool {
return identical(x, y, true, nil)
}
// IdenticalIgnoreTags reports whether x and y are identical types if tags are ignored.
// Receivers of Signature types are ignored.
func IdenticalIgnoreTags(x, y Type) bool {
return identical(x, y, false, nil)
}
// An ifacePair is a node in a stack of interface type pairs compared for identity.
type ifacePair struct {
x, y *Interface
prev *ifacePair
}
func (p *ifacePair) identical(q *ifacePair) bool {
return p.x == q.x && p.y == q.y || p.x == q.y && p.y == q.x
}
func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
if x == y {
return true
}
switch x := x.(type) {
case *Basic:
// Basic types are singletons except for the rune and byte
// aliases, thus we cannot solely rely on the x == y check
// above. See also comment in TypeName.IsAlias.
if y, ok := y.(*Basic); ok {
return x.kind == y.kind
}
case *Array:
// Two array types are identical if they have identical element types
// and the same array length.
if y, ok := y.(*Array); ok {
// If one or both array lengths are unknown (< 0) due to some error,
// assume they are the same to avoid spurious follow-on errors.
return (x.len < 0 || y.len < 0 || x.len == y.len) && identical(x.elem, y.elem, cmpTags, p)
}
case *Slice:
// Two slice types are identical if they have identical element types.
if y, ok := y.(*Slice); ok {
return identical(x.elem, y.elem, cmpTags, p)
}
case *Struct:
// Two struct types are identical if they have the same sequence of fields,
// and if corresponding fields have the same names, and identical types,
// and identical tags. Two embedded fields are considered to have the same
// name. Lower-case field names from different packages are always different.
if y, ok := y.(*Struct); ok {
if x.NumFields() == y.NumFields() {
for i, f := range x.fields {
g := y.fields[i]
if f.embedded != g.embedded ||
cmpTags && x.Tag(i) != y.Tag(i) ||
!f.sameId(g.pkg, g.name) ||
!identical(f.typ, g.typ, cmpTags, p) {
return false
}
}
return true
}
}
case *Pointer:
// Two pointer types are identical if they have identical base types.
if y, ok := y.(*Pointer); ok {
return identical(x.base, y.base, cmpTags, p)
}
case *Tuple:
// Two tuples types are identical if they have the same number of elements
// and corresponding elements have identical types.
if y, ok := y.(*Tuple); ok {
if x.Len() == y.Len() {
if x != nil {
for i, v := range x.vars {
w := y.vars[i]
if !identical(v.typ, w.typ, cmpTags, p) {
return false
}
}
}
return true
}
}
case *Signature:
// Two function types are identical if they have the same number of parameters
// and result values, corresponding parameter and result types are identical,
// and either both functions are variadic or neither is. Parameter and result
// names are not required to match.
if y, ok := y.(*Signature); ok {
return x.variadic == y.variadic &&
identical(x.params, y.params, cmpTags, p) &&
identical(x.results, y.results, cmpTags, p)
}
case *Interface:
// Two interface types are identical if they have the same set of methods with
// the same names and identical function types. Lower-case method names from
// different packages are always different. The order of the methods is irrelevant.
if y, ok := y.(*Interface); ok {
a := x.allMethods
b := y.allMethods
if len(a) == len(b) {
// Interface types are the only types where cycles can occur
// that are not "terminated" via named types; and such cycles
// can only be created via method parameter types that are
// anonymous interfaces (directly or indirectly) embedding
// the current interface. Example:
//
// type T interface {
// m() interface{T}
// }
//
// If two such (differently named) interfaces are compared,
// endless recursion occurs if the cycle is not detected.
//
// If x and y were compared before, they must be equal
// (if they were not, the recursion would have stopped);
// search the ifacePair stack for the same pair.
//
// This is a quadratic algorithm, but in practice these stacks
// are extremely short (bounded by the nesting depth of interface
// type declarations that recur via parameter types, an extremely
// rare occurrence). An alternative implementation might use a
// "visited" map, but that is probably less efficient overall.
q := &ifacePair{x, y, p}
for p != nil {
if p.identical(q) {
return true // same pair was compared before
}
p = p.prev
}
if debug {
assert(sort.IsSorted(byUniqueMethodName(a)))
assert(sort.IsSorted(byUniqueMethodName(b)))
}
for i, f := range a {
g := b[i]
if f.Id() != g.Id() || !identical(f.typ, g.typ, cmpTags, q) {
return false
}
}
return true
}
}
case *Map:
// Two map types are identical if they have identical key and value types.
if y, ok := y.(*Map); ok {
return identical(x.key, y.key, cmpTags, p) && identical(x.elem, y.elem, cmpTags, p)
}
case *Chan:
// Two channel types are identical if they have identical value types
// and the same direction.
if y, ok := y.(*Chan); ok {
return x.dir == y.dir && identical(x.elem, y.elem, cmpTags, p)
}
case *Named:
// Two named types are identical if their type names originate
// in the same type declaration.
if y, ok := y.(*Named); ok {
return x.obj == y.obj
}
case nil:
default:
unreachable()
}
return false
}
// Default returns the default "typed" type for an "untyped" type;
// it returns the incoming type for all other types. The default type
// for untyped nil is untyped nil.
//
func Default(typ Type) Type {
if t, ok := typ.(*Basic); ok {
switch t.kind {
case UntypedBool:
return Typ[Bool]
case UntypedInt:
return Typ[Int]
case UntypedRune:
return universeRune // use 'rune' name
case UntypedFloat:
return Typ[Float64]
case UntypedComplex:
return Typ[Complex128]
case UntypedString:
return Typ[String]
}
}
return typ
}