go/types/predicates.go

// 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

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
}

func isInterface(typ Type) bool {
	_, ok := typ.Underlying().(*Interface)
	return ok
}

func isComparable(typ Type) bool {
	switch t := typ.Underlying().(type) {
	case *Basic:
		return t.kind != Invalid && t.kind != UntypedNil
	case *Pointer, *Interface, *Chan:
		// assumes types are equal for pointers and channels
		return true
	case *Struct:
		for _, f := range t.fields {
			if !isComparable(f.typ) {
				return false
			}
		}
		return true
	case *Array:
		return isComparable(t.elt)
	}
	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
}

// IsIdentical returns true if x and y are identical.
func IsIdentical(x, y Type) 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.
		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 {
			return x.len == y.len && IsIdentical(x.elt, y.elt)
		}

	case *Slice:
		// Two slice types are identical if they have identical element types.
		if y, ok := y.(*Slice); ok {
			return IsIdentical(x.elt, y.elt)
		}

	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 anonymous 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.anonymous != g.anonymous ||
						x.Tag(i) != y.Tag(i) ||
						!f.sameId(g.pkg, g.name) ||
						!IsIdentical(f.typ, g.typ) {
						return false
					}
				}
				return true
			}
		}

	case *Pointer:
		// Two pointer types are identical if they have identical base types.
		if y, ok := y.(*Pointer); ok {
			return IsIdentical(x.base, y.base)
		}

	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 {
			return identicalTuples(x, y)
		}

	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.isVariadic == y.isVariadic &&
				identicalTuples(x.params, y.params) &&
				identicalTuples(x.results, y.results)
		}

	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 {
			return identicalMethods(x.methods, y.methods) // methods are sorted
		}

	case *Map:
		// Two map types are identical if they have identical key and value types.
		if y, ok := y.(*Map); ok {
			return IsIdentical(x.key, y.key) && IsIdentical(x.elt, y.elt)
		}

	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 && IsIdentical(x.elt, y.elt)
		}

	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
		}
	}

	return false
}

// identicalTuples returns true if both tuples a and b have the
// same length and corresponding elements have identical types.
func identicalTuples(a, b *Tuple) bool {
	if a.Len() != b.Len() {
		return false
	}
	if a != nil {
		for i, x := range a.vars {
			y := b.vars[i]
			if !IsIdentical(x.typ, y.typ) {
				return false
			}
		}
	}
	return true
}

// identicalMethods returns true if both slices a and b have the
// same length and corresponding entries have identical types.
// TODO(gri) make this more efficient (e.g., sort them on completion)
func identicalMethods(a, b []*Func) bool {
	if len(a) != len(b) {
		return false
	}

	m := make(map[string]*Func)
	for _, x := range a {
		key := x.Id()
		assert(m[key] == nil) // method list must not have duplicate entries
		m[key] = x
	}

	for _, y := range b {
		key := y.Id()
		if x := m[key]; x == nil || !IsIdentical(x.typ, y.typ) {
			return false
		}
	}

	return true
}

// defaultType 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 defaultType(typ Type) Type {
	if t, ok := typ.(*Basic); ok {
		k := t.kind
		switch k {
		case UntypedBool:
			k = Bool
		case UntypedInt:
			k = Int
		case UntypedRune:
			k = Rune
		case UntypedFloat:
			k = Float64
		case UntypedComplex:
			k = Complex128
		case UntypedString:
			k = String
		}
		typ = Typ[k]
	}
	return typ
}