predicates.go

Documentation: go/types

		 1  // Copyright 2012 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  // This file implements commonly used type predicates.
		 6  
		 7  package types
		 8  
		 9  import (
		10  	"go/token"
		11  )
		12  
		13  // isNamed reports whether typ has a name.
		14  // isNamed may be called with types that are not fully set up.
		15  func isNamed(typ Type) bool {
		16  	switch typ.(type) {
		17  	case *Basic, *Named, *_TypeParam, *instance:
		18  		return true
		19  	}
		20  	return false
		21  }
		22  
		23  // isGeneric reports whether a type is a generic, uninstantiated type (generic
		24  // signatures are not included).
		25  func isGeneric(typ Type) bool {
		26  	// A parameterized type is only instantiated if it doesn't have an instantiation already.
		27  	named, _ := typ.(*Named)
		28  	return named != nil && named.obj != nil && named.tparams != nil && named.targs == nil
		29  }
		30  
		31  func is(typ Type, what BasicInfo) bool {
		32  	switch t := optype(typ).(type) {
		33  	case *Basic:
		34  		return t.info&what != 0
		35  	case *_Sum:
		36  		return t.is(func(typ Type) bool { return is(typ, what) })
		37  	}
		38  	return false
		39  }
		40  
		41  func isBoolean(typ Type) bool	{ return is(typ, IsBoolean) }
		42  func isInteger(typ Type) bool	{ return is(typ, IsInteger) }
		43  func isUnsigned(typ Type) bool { return is(typ, IsUnsigned) }
		44  func isFloat(typ Type) bool		{ return is(typ, IsFloat) }
		45  func isComplex(typ Type) bool	{ return is(typ, IsComplex) }
		46  func isNumeric(typ Type) bool	{ return is(typ, IsNumeric) }
		47  func isString(typ Type) bool	 { return is(typ, IsString) }
		48  
		49  // Note that if typ is a type parameter, isInteger(typ) || isFloat(typ) does not
		50  // produce the expected result because a type list that contains both an integer
		51  // and a floating-point type is neither (all) integers, nor (all) floats.
		52  // Use isIntegerOrFloat instead.
		53  func isIntegerOrFloat(typ Type) bool { return is(typ, IsInteger|IsFloat) }
		54  
		55  // isNumericOrString is the equivalent of isIntegerOrFloat for isNumeric(typ) || isString(typ).
		56  func isNumericOrString(typ Type) bool { return is(typ, IsNumeric|IsString) }
		57  
		58  // isTyped reports whether typ is typed; i.e., not an untyped
		59  // constant or boolean. isTyped may be called with types that
		60  // are not fully set up.
		61  func isTyped(typ Type) bool {
		62  	// isTyped is called with types that are not fully
		63  	// set up. Must not call asBasic()!
		64  	// A *Named or *instance type is always typed, so
		65  	// we only need to check if we have a true *Basic
		66  	// type.
		67  	t, _ := typ.(*Basic)
		68  	return t == nil || t.info&IsUntyped == 0
		69  }
		70  
		71  // isUntyped(typ) is the same as !isTyped(typ).
		72  func isUntyped(typ Type) bool {
		73  	return !isTyped(typ)
		74  }
		75  
		76  func isOrdered(typ Type) bool { return is(typ, IsOrdered) }
		77  
		78  func isConstType(typ Type) bool {
		79  	// Type parameters are never const types.
		80  	t, _ := under(typ).(*Basic)
		81  	return t != nil && t.info&IsConstType != 0
		82  }
		83  
		84  // IsInterface reports whether typ is an interface type.
		85  func IsInterface(typ Type) bool {
		86  	return asInterface(typ) != nil
		87  }
		88  
		89  // Comparable reports whether values of type T are comparable.
		90  func Comparable(T Type) bool {
		91  	return comparable(T, nil)
		92  }
		93  
		94  func comparable(T Type, seen map[Type]bool) bool {
		95  	if seen[T] {
		96  		return true
		97  	}
		98  	if seen == nil {
		99  		seen = make(map[Type]bool)
	 100  	}
	 101  	seen[T] = true
	 102  
	 103  	// If T is a type parameter not constrained by any type
	 104  	// list (i.e., it's underlying type is the top type),
	 105  	// T is comparable if it has the == method. Otherwise,
	 106  	// the underlying type "wins". For instance
	 107  	//
	 108  	//		 interface{ comparable; type []byte }
	 109  	//
	 110  	// is not comparable because []byte is not comparable.
	 111  	if t := asTypeParam(T); t != nil && optype(t) == theTop {
	 112  		return t.Bound()._IsComparable()
	 113  	}
	 114  
	 115  	switch t := optype(T).(type) {
	 116  	case *Basic:
	 117  		// assume invalid types to be comparable
	 118  		// to avoid follow-up errors
	 119  		return t.kind != UntypedNil
	 120  	case *Pointer, *Interface, *Chan:
	 121  		return true
	 122  	case *Struct:
	 123  		for _, f := range t.fields {
	 124  			if !comparable(f.typ, seen) {
	 125  				return false
	 126  			}
	 127  		}
	 128  		return true
	 129  	case *Array:
	 130  		return comparable(t.elem, seen)
	 131  	case *_Sum:
	 132  		pred := func(t Type) bool {
	 133  			return comparable(t, seen)
	 134  		}
	 135  		return t.is(pred)
	 136  	case *_TypeParam:
	 137  		return t.Bound()._IsComparable()
	 138  	}
	 139  	return false
	 140  }
	 141  
	 142  // hasNil reports whether a type includes the nil value.
	 143  func hasNil(typ Type) bool {
	 144  	switch t := optype(typ).(type) {
	 145  	case *Basic:
	 146  		return t.kind == UnsafePointer
	 147  	case *Slice, *Pointer, *Signature, *Interface, *Map, *Chan:
	 148  		return true
	 149  	case *_Sum:
	 150  		return t.is(hasNil)
	 151  	}
	 152  	return false
	 153  }
	 154  
	 155  // identical reports whether x and y are identical types.
	 156  // Receivers of Signature types are ignored.
	 157  func (check *Checker) identical(x, y Type) bool {
	 158  	return check.identical0(x, y, true, nil)
	 159  }
	 160  
	 161  // identicalIgnoreTags reports whether x and y are identical types if tags are ignored.
	 162  // Receivers of Signature types are ignored.
	 163  func (check *Checker) identicalIgnoreTags(x, y Type) bool {
	 164  	return check.identical0(x, y, false, nil)
	 165  }
	 166  
	 167  // An ifacePair is a node in a stack of interface type pairs compared for identity.
	 168  type ifacePair struct {
	 169  	x, y *Interface
	 170  	prev *ifacePair
	 171  }
	 172  
	 173  func (p *ifacePair) identical(q *ifacePair) bool {
	 174  	return p.x == q.x && p.y == q.y || p.x == q.y && p.y == q.x
	 175  }
	 176  
	 177  // For changes to this code the corresponding changes should be made to unifier.nify.
	 178  func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
	 179  	// types must be expanded for comparison
	 180  	x = expandf(x)
	 181  	y = expandf(y)
	 182  
	 183  	if x == y {
	 184  		return true
	 185  	}
	 186  
	 187  	switch x := x.(type) {
	 188  	case *Basic:
	 189  		// Basic types are singletons except for the rune and byte
	 190  		// aliases, thus we cannot solely rely on the x == y check
	 191  		// above. See also comment in TypeName.IsAlias.
	 192  		if y, ok := y.(*Basic); ok {
	 193  			return x.kind == y.kind
	 194  		}
	 195  
	 196  	case *Array:
	 197  		// Two array types are identical if they have identical element types
	 198  		// and the same array length.
	 199  		if y, ok := y.(*Array); ok {
	 200  			// If one or both array lengths are unknown (< 0) due to some error,
	 201  			// assume they are the same to avoid spurious follow-on errors.
	 202  			return (x.len < 0 || y.len < 0 || x.len == y.len) && check.identical0(x.elem, y.elem, cmpTags, p)
	 203  		}
	 204  
	 205  	case *Slice:
	 206  		// Two slice types are identical if they have identical element types.
	 207  		if y, ok := y.(*Slice); ok {
	 208  			return check.identical0(x.elem, y.elem, cmpTags, p)
	 209  		}
	 210  
	 211  	case *Struct:
	 212  		// Two struct types are identical if they have the same sequence of fields,
	 213  		// and if corresponding fields have the same names, and identical types,
	 214  		// and identical tags. Two embedded fields are considered to have the same
	 215  		// name. Lower-case field names from different packages are always different.
	 216  		if y, ok := y.(*Struct); ok {
	 217  			if x.NumFields() == y.NumFields() {
	 218  				for i, f := range x.fields {
	 219  					g := y.fields[i]
	 220  					if f.embedded != g.embedded ||
	 221  						cmpTags && x.Tag(i) != y.Tag(i) ||
	 222  						!f.sameId(g.pkg, g.name) ||
	 223  						!check.identical0(f.typ, g.typ, cmpTags, p) {
	 224  						return false
	 225  					}
	 226  				}
	 227  				return true
	 228  			}
	 229  		}
	 230  
	 231  	case *Pointer:
	 232  		// Two pointer types are identical if they have identical base types.
	 233  		if y, ok := y.(*Pointer); ok {
	 234  			return check.identical0(x.base, y.base, cmpTags, p)
	 235  		}
	 236  
	 237  	case *Tuple:
	 238  		// Two tuples types are identical if they have the same number of elements
	 239  		// and corresponding elements have identical types.
	 240  		if y, ok := y.(*Tuple); ok {
	 241  			if x.Len() == y.Len() {
	 242  				if x != nil {
	 243  					for i, v := range x.vars {
	 244  						w := y.vars[i]
	 245  						if !check.identical0(v.typ, w.typ, cmpTags, p) {
	 246  							return false
	 247  						}
	 248  					}
	 249  				}
	 250  				return true
	 251  			}
	 252  		}
	 253  
	 254  	case *Signature:
	 255  		// Two function types are identical if they have the same number of parameters
	 256  		// and result values, corresponding parameter and result types are identical,
	 257  		// and either both functions are variadic or neither is. Parameter and result
	 258  		// names are not required to match.
	 259  		// Generic functions must also have matching type parameter lists, but for the
	 260  		// parameter names.
	 261  		if y, ok := y.(*Signature); ok {
	 262  			return x.variadic == y.variadic &&
	 263  				check.identicalTParams(x.tparams, y.tparams, cmpTags, p) &&
	 264  				check.identical0(x.params, y.params, cmpTags, p) &&
	 265  				check.identical0(x.results, y.results, cmpTags, p)
	 266  		}
	 267  
	 268  	case *_Sum:
	 269  		// Two sum types are identical if they contain the same types.
	 270  		// (Sum types always consist of at least two types. Also, the
	 271  		// the set (list) of types in a sum type consists of unique
	 272  		// types - each type appears exactly once. Thus, two sum types
	 273  		// must contain the same number of types to have chance of
	 274  		// being equal.
	 275  		if y, ok := y.(*_Sum); ok && len(x.types) == len(y.types) {
	 276  			// Every type in x.types must be in y.types.
	 277  			// Quadratic algorithm, but probably good enough for now.
	 278  			// TODO(gri) we need a fast quick type ID/hash for all types.
	 279  		L:
	 280  			for _, x := range x.types {
	 281  				for _, y := range y.types {
	 282  					if Identical(x, y) {
	 283  						continue L // x is in y.types
	 284  					}
	 285  				}
	 286  				return false // x is not in y.types
	 287  			}
	 288  			return true
	 289  		}
	 290  
	 291  	case *Interface:
	 292  		// Two interface types are identical if they have the same set of methods with
	 293  		// the same names and identical function types. Lower-case method names from
	 294  		// different packages are always different. The order of the methods is irrelevant.
	 295  		if y, ok := y.(*Interface); ok {
	 296  			// If identical0 is called (indirectly) via an external API entry point
	 297  			// (such as Identical, IdenticalIgnoreTags, etc.), check is nil. But in
	 298  			// that case, interfaces are expected to be complete and lazy completion
	 299  			// here is not needed.
	 300  			if check != nil {
	 301  				check.completeInterface(token.NoPos, x)
	 302  				check.completeInterface(token.NoPos, y)
	 303  			}
	 304  			a := x.allMethods
	 305  			b := y.allMethods
	 306  			if len(a) == len(b) {
	 307  				// Interface types are the only types where cycles can occur
	 308  				// that are not "terminated" via named types; and such cycles
	 309  				// can only be created via method parameter types that are
	 310  				// anonymous interfaces (directly or indirectly) embedding
	 311  				// the current interface. Example:
	 312  				//
	 313  				//		type T interface {
	 314  				//				m() interface{T}
	 315  				//		}
	 316  				//
	 317  				// If two such (differently named) interfaces are compared,
	 318  				// endless recursion occurs if the cycle is not detected.
	 319  				//
	 320  				// If x and y were compared before, they must be equal
	 321  				// (if they were not, the recursion would have stopped);
	 322  				// search the ifacePair stack for the same pair.
	 323  				//
	 324  				// This is a quadratic algorithm, but in practice these stacks
	 325  				// are extremely short (bounded by the nesting depth of interface
	 326  				// type declarations that recur via parameter types, an extremely
	 327  				// rare occurrence). An alternative implementation might use a
	 328  				// "visited" map, but that is probably less efficient overall.
	 329  				q := &ifacePair{x, y, p}
	 330  				for p != nil {
	 331  					if p.identical(q) {
	 332  						return true // same pair was compared before
	 333  					}
	 334  					p = p.prev
	 335  				}
	 336  				if debug {
	 337  					assertSortedMethods(a)
	 338  					assertSortedMethods(b)
	 339  				}
	 340  				for i, f := range a {
	 341  					g := b[i]
	 342  					if f.Id() != g.Id() || !check.identical0(f.typ, g.typ, cmpTags, q) {
	 343  						return false
	 344  					}
	 345  				}
	 346  				return true
	 347  			}
	 348  		}
	 349  
	 350  	case *Map:
	 351  		// Two map types are identical if they have identical key and value types.
	 352  		if y, ok := y.(*Map); ok {
	 353  			return check.identical0(x.key, y.key, cmpTags, p) && check.identical0(x.elem, y.elem, cmpTags, p)
	 354  		}
	 355  
	 356  	case *Chan:
	 357  		// Two channel types are identical if they have identical value types
	 358  		// and the same direction.
	 359  		if y, ok := y.(*Chan); ok {
	 360  			return x.dir == y.dir && check.identical0(x.elem, y.elem, cmpTags, p)
	 361  		}
	 362  
	 363  	case *Named:
	 364  		// Two named types are identical if their type names originate
	 365  		// in the same type declaration.
	 366  		if y, ok := y.(*Named); ok {
	 367  			// TODO(gri) Why is x == y not sufficient? And if it is,
	 368  			//					 we can just return false here because x == y
	 369  			//					 is caught in the very beginning of this function.
	 370  			return x.obj == y.obj
	 371  		}
	 372  
	 373  	case *_TypeParam:
	 374  		// nothing to do (x and y being equal is caught in the very beginning of this function)
	 375  
	 376  	// case *instance:
	 377  	//	unreachable since types are expanded
	 378  
	 379  	case *bottom, *top:
	 380  		// Either both types are theBottom, or both are theTop in which
	 381  		// case the initial x == y check will have caught them. Otherwise
	 382  		// they are not identical.
	 383  
	 384  	case nil:
	 385  		// avoid a crash in case of nil type
	 386  
	 387  	default:
	 388  		unreachable()
	 389  	}
	 390  
	 391  	return false
	 392  }
	 393  
	 394  func (check *Checker) identicalTParams(x, y []*TypeName, cmpTags bool, p *ifacePair) bool {
	 395  	if len(x) != len(y) {
	 396  		return false
	 397  	}
	 398  	for i, x := range x {
	 399  		y := y[i]
	 400  		if !check.identical0(x.typ.(*_TypeParam).bound, y.typ.(*_TypeParam).bound, cmpTags, p) {
	 401  			return false
	 402  		}
	 403  	}
	 404  	return true
	 405  }
	 406  
	 407  // Default returns the default "typed" type for an "untyped" type;
	 408  // it returns the incoming type for all other types. The default type
	 409  // for untyped nil is untyped nil.
	 410  //
	 411  func Default(typ Type) Type {
	 412  	if t, ok := typ.(*Basic); ok {
	 413  		switch t.kind {
	 414  		case UntypedBool:
	 415  			return Typ[Bool]
	 416  		case UntypedInt:
	 417  			return Typ[Int]
	 418  		case UntypedRune:
	 419  			return universeRune // use 'rune' name
	 420  		case UntypedFloat:
	 421  			return Typ[Float64]
	 422  		case UntypedComplex:
	 423  			return Typ[Complex128]
	 424  		case UntypedString:
	 425  			return Typ[String]
	 426  		}
	 427  	}
	 428  	return typ
	 429  }
	 430
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