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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 (
"go/token"
)
// isNamed reports whether typ has a name.
// isNamed may be called with types that are not fully set up.
func isNamed(typ Type) bool {
switch typ.(type) {
case *Basic, *Named, *_TypeParam, *instance:
return true
}
return false
}
// isGeneric reports whether a type is a generic, uninstantiated type (generic
// signatures are not included).
func isGeneric(typ Type) bool {
// A parameterized type is only instantiated if it doesn't have an instantiation already.
named, _ := typ.(*Named)
return named != nil && named.obj != nil && named.tparams != nil && named.targs == nil
}
func is(typ Type, what BasicInfo) bool {
switch t := optype(typ).(type) {
case *Basic:
return t.info&what != 0
case *_Sum:
return t.is(func(typ Type) bool { return is(typ, what) })
}
return false
}
func isBoolean(typ Type) bool { return is(typ, IsBoolean) }
func isInteger(typ Type) bool { return is(typ, IsInteger) }
func isUnsigned(typ Type) bool { return is(typ, IsUnsigned) }
func isFloat(typ Type) bool { return is(typ, IsFloat) }
func isComplex(typ Type) bool { return is(typ, IsComplex) }
func isNumeric(typ Type) bool { return is(typ, IsNumeric) }
func isString(typ Type) bool { return is(typ, IsString) }
// Note that if typ is a type parameter, isInteger(typ) || isFloat(typ) does not
// produce the expected result because a type list that contains both an integer
// and a floating-point type is neither (all) integers, nor (all) floats.
// Use isIntegerOrFloat instead.
func isIntegerOrFloat(typ Type) bool { return is(typ, IsInteger|IsFloat) }
// isNumericOrString is the equivalent of isIntegerOrFloat for isNumeric(typ) || isString(typ).
func isNumericOrString(typ Type) bool { return is(typ, IsNumeric|IsString) }
// isTyped reports whether typ is typed; i.e., not an untyped
// constant or boolean. isTyped may be called with types that
// are not fully set up.
func isTyped(typ Type) bool {
// isTyped is called with types that are not fully
// set up. Must not call asBasic()!
// A *Named or *instance type is always typed, so
// we only need to check if we have a true *Basic
// type.
t, _ := typ.(*Basic)
return t == nil || t.info&IsUntyped == 0
}
// isUntyped(typ) is the same as !isTyped(typ).
func isUntyped(typ Type) bool {
return !isTyped(typ)
}
func isOrdered(typ Type) bool { return is(typ, IsOrdered) }
func isConstType(typ Type) bool {
// Type parameters are never const types.
t, _ := under(typ).(*Basic)
return t != nil && t.info&IsConstType != 0
}
// IsInterface reports whether typ is an interface type.
func IsInterface(typ Type) bool {
return asInterface(typ) != nil
}
// Comparable reports whether values of type T are comparable.
func Comparable(T Type) bool {
return comparable(T, nil)
}
func comparable(T Type, seen map[Type]bool) bool {
if seen[T] {
return true
}
if seen == nil {
seen = make(map[Type]bool)
}
seen[T] = true
// If T is a type parameter not constrained by any type
// list (i.e., it's underlying type is the top type),
// T is comparable if it has the == method. Otherwise,
// the underlying type "wins". For instance
//
// interface{ comparable; type []byte }
//
// is not comparable because []byte is not comparable.
if t := asTypeParam(T); t != nil && optype(t) == theTop {
return t.Bound()._IsComparable()
}
switch t := optype(T).(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, seen) {
return false
}
}
return true
case *Array:
return comparable(t.elem, seen)
case *_Sum:
pred := func(t Type) bool {
return comparable(t, seen)
}
return t.is(pred)
case *_TypeParam:
return t.Bound()._IsComparable()
}
return false
}
// hasNil reports whether a type includes the nil value.
func hasNil(typ Type) bool {
switch t := optype(typ).(type) {
case *Basic:
return t.kind == UnsafePointer
case *Slice, *Pointer, *Signature, *Interface, *Map, *Chan:
return true
case *_Sum:
return t.is(hasNil)
}
return false
}
// identical reports whether x and y are identical types.
// Receivers of Signature types are ignored.
func (check *Checker) identical(x, y Type) bool {
return check.identical0(x, y, true, nil)
}
// identicalIgnoreTags reports whether x and y are identical types if tags are ignored.
// Receivers of Signature types are ignored.
func (check *Checker) identicalIgnoreTags(x, y Type) bool {
return check.identical0(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
}
// For changes to this code the corresponding changes should be made to unifier.nify.
func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
// types must be expanded for comparison
x = expandf(x)
y = expandf(y)
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) && check.identical0(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 check.identical0(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) ||
!check.identical0(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 check.identical0(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 !check.identical0(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.
// Generic functions must also have matching type parameter lists, but for the
// parameter names.
if y, ok := y.(*Signature); ok {
return x.variadic == y.variadic &&
check.identicalTParams(x.tparams, y.tparams, cmpTags, p) &&
check.identical0(x.params, y.params, cmpTags, p) &&
check.identical0(x.results, y.results, cmpTags, p)
}
case *_Sum:
// Two sum types are identical if they contain the same types.
// (Sum types always consist of at least two types. Also, the
// the set (list) of types in a sum type consists of unique
// types - each type appears exactly once. Thus, two sum types
// must contain the same number of types to have chance of
// being equal.
if y, ok := y.(*_Sum); ok && len(x.types) == len(y.types) {
// Every type in x.types must be in y.types.
// Quadratic algorithm, but probably good enough for now.
// TODO(gri) we need a fast quick type ID/hash for all types.
L:
for _, x := range x.types {
for _, y := range y.types {
if Identical(x, y) {
continue L // x is in y.types
}
}
return false // x is not in y.types
}
return true
}
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 {
// If identical0 is called (indirectly) via an external API entry point
// (such as Identical, IdenticalIgnoreTags, etc.), check is nil. But in
// that case, interfaces are expected to be complete and lazy completion
// here is not needed.
if check != nil {
check.completeInterface(token.NoPos, x)
check.completeInterface(token.NoPos, y)
}
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 {
assertSortedMethods(a)
assertSortedMethods(b)
}
for i, f := range a {
g := b[i]
if f.Id() != g.Id() || !check.identical0(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 check.identical0(x.key, y.key, cmpTags, p) && check.identical0(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 && check.identical0(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 {
// TODO(gri) Why is x == y not sufficient? And if it is,
// we can just return false here because x == y
// is caught in the very beginning of this function.
return x.obj == y.obj
}
case *_TypeParam:
// nothing to do (x and y being equal is caught in the very beginning of this function)
// case *instance:
// unreachable since types are expanded
case *bottom, *top:
// Either both types are theBottom, or both are theTop in which
// case the initial x == y check will have caught them. Otherwise
// they are not identical.
case nil:
// avoid a crash in case of nil type
default:
unreachable()
}
return false
}
func (check *Checker) identicalTParams(x, y []*TypeName, cmpTags bool, p *ifacePair) bool {
if len(x) != len(y) {
return false
}
for i, x := range x {
y := y[i]
if !check.identical0(x.typ.(*_TypeParam).bound, y.typ.(*_TypeParam).bound, cmpTags, p) {
return false
}
}
return true
}
// 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
}