1 // Copyright 2013 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.
5 // This file implements various field and method lookup functions.
11 // Internal use of LookupFieldOrMethod: If the obj result is a method
12 // associated with a concrete (non-interface) type, the method's signature
13 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
16 // LookupFieldOrMethod looks up a field or method with given package and name
17 // in T and returns the corresponding *Var or *Func, an index sequence, and a
18 // bool indicating if there were any pointer indirections on the path to the
19 // field or method. If addressable is set, T is the type of an addressable
20 // variable (only matters for method lookups).
22 // The last index entry is the field or method index in the (possibly embedded)
23 // type where the entry was found, either:
25 // 1) the list of declared methods of a named type; or
26 // 2) the list of all methods (method set) of an interface type; or
27 // 3) the list of fields of a struct type.
29 // The earlier index entries are the indices of the embedded struct fields
30 // traversed to get to the found entry, starting at depth 0.
32 // If no entry is found, a nil object is returned. In this case, the returned
33 // index and indirect values have the following meaning:
35 // - If index != nil, the index sequence points to an ambiguous entry
36 // (the same name appeared more than once at the same embedding level).
38 // - If indirect is set, a method with a pointer receiver type was found
39 // but there was no pointer on the path from the actual receiver type to
40 // the method's formal receiver base type, nor was the receiver addressable.
42 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
43 // Methods cannot be associated to a named pointer type
44 // (spec: "The type denoted by T is called the receiver base type;
45 // it must not be a pointer or interface type and it must be declared
46 // in the same package as the method.").
47 // Thus, if we have a named pointer type, proceed with the underlying
48 // pointer type but discard the result if it is a method since we would
49 // not have found it for T (see also issue 8590).
50 if t := asNamed(T); t != nil {
51 if p, _ := t.Underlying().(*Pointer); p != nil {
52 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
53 if _, ok := obj.(*Func); ok {
54 return nil, nil, false
60 return lookupFieldOrMethod(T, addressable, pkg, name)
63 // TODO(gri) The named type consolidation and seen maps below must be
64 // indexed by unique keys for a given type. Verify that named
65 // types always have only one representation (even when imported
66 // indirectly via different packages.)
68 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
69 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
70 // WARNING: The code in this function is extremely subtle - do not modify casually!
73 return // blank fields/methods are never found
76 typ, isPtr := deref(T)
78 // *typ where typ is an interface or type parameter has no methods.
79 switch under(typ).(type) {
80 case *Interface, *TypeParam:
86 // Start with typ as single entry at shallowest depth.
87 current := []embeddedType{{typ, nil, isPtr, false}}
89 // Named types that we have seen already, allocated lazily.
90 // Used to avoid endless searches in case of recursive types.
91 // Since only Named types can be used for recursive types, we
92 // only need to track those.
93 // (If we ever allow type aliases to construct recursive types,
94 // we must use type identity rather than pointer equality for
95 // the map key comparison, as we do in consolidateMultiples.)
96 var seen map[*Named]bool
98 // search current depth
99 for len(current) > 0 {
100 var next []embeddedType // embedded types found at current depth
102 // look for (pkg, name) in all types at current depth
103 var tpar *TypeParam // set if obj receiver is a type parameter
104 for _, e := range current {
107 // If we have a named type, we may have associated methods.
108 // Look for those first.
109 if named := asNamed(typ); named != nil {
111 // We have seen this type before, at a more shallow depth
112 // (note that multiples of this type at the current depth
113 // were consolidated before). The type at that depth shadows
114 // this same type at the current depth, so we can ignore
119 seen = make(map[*Named]bool)
123 // look for a matching attached method
125 if i, m := lookupMethod(named.methods, pkg, name); m != nil {
127 // caution: method may not have a proper signature yet
128 index = concat(e.index, i)
129 if obj != nil || e.multiples {
130 return nil, index, false // collision
133 indirect = e.indirect
134 continue // we can't have a matching field or interface method
137 // continue with underlying type, but only if it's not a type parameter
138 // TODO(gri) is this what we want to do for type parameters? (spec question)
139 // TODO(#45639) the error message produced as a result of skipping an
140 // underlying type parameter should be improved.
142 if asTypeParam(typ) != nil {
148 switch t := typ.(type) {
150 // look for a matching field and collect embedded types
151 for i, f := range t.fields {
152 if f.sameId(pkg, name) {
154 index = concat(e.index, i)
155 if obj != nil || e.multiples {
156 return nil, index, false // collision
159 indirect = e.indirect
160 continue // we can't have a matching interface method
162 // Collect embedded struct fields for searching the next
163 // lower depth, but only if we have not seen a match yet
164 // (if we have a match it is either the desired field or
165 // we have a name collision on the same depth; in either
166 // case we don't need to look further).
167 // Embedded fields are always of the form T or *T where
168 // T is a type name. If e.typ appeared multiple times at
169 // this depth, f.typ appears multiple times at the next
171 if obj == nil && f.embedded {
172 typ, isPtr := deref(f.typ)
173 // TODO(gri) optimization: ignore types that can't
174 // have fields or methods (only Named, Struct, and
175 // Interface types need to be considered).
176 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
181 // look for a matching method
182 if i, m := t.typeSet().LookupMethod(pkg, name); m != nil {
184 index = concat(e.index, i)
185 if obj != nil || e.multiples {
186 return nil, index, false // collision
189 indirect = e.indirect
193 if i, m := t.Bound().typeSet().LookupMethod(pkg, name); m != nil {
195 index = concat(e.index, i)
196 if obj != nil || e.multiples {
197 return nil, index, false // collision
201 indirect = e.indirect
207 // found a potential match
208 // spec: "A method call x.m() is valid if the method set of (the type of) x
209 // contains m and the argument list can be assigned to the parameter
210 // list of m. If x is addressable and &x's method set contains m, x.m()
211 // is shorthand for (&x).m()".
212 if f, _ := obj.(*Func); f != nil {
213 // determine if method has a pointer receiver
214 hasPtrRecv := tpar == nil && ptrRecv(f)
215 if hasPtrRecv && !indirect && !addressable {
216 return nil, nil, true // pointer/addressable receiver required
222 current = consolidateMultiples(next)
225 return nil, nil, false // not found
228 // embeddedType represents an embedded type
229 type embeddedType struct {
231 index []int // embedded field indices, starting with index at depth 0
232 indirect bool // if set, there was a pointer indirection on the path to this field
233 multiples bool // if set, typ appears multiple times at this depth
236 // consolidateMultiples collects multiple list entries with the same type
237 // into a single entry marked as containing multiples. The result is the
238 // consolidated list.
239 func consolidateMultiples(list []embeddedType) []embeddedType {
241 return list // at most one entry - nothing to do
244 n := 0 // number of entries w/ unique type
245 prev := make(map[Type]int) // index at which type was previously seen
246 for _, e := range list {
247 if i, found := lookupType(prev, e.typ); found {
248 list[i].multiples = true
259 func lookupType(m map[Type]int, typ Type) (int, bool) {
260 // fast path: maybe the types are equal
261 if i, found := m[typ]; found {
265 for t, i := range m {
266 if Identical(t, typ) {
274 // MissingMethod returns (nil, false) if V implements T, otherwise it
275 // returns a missing method required by T and whether it is missing or
276 // just has the wrong type.
278 // For non-interface types V, or if static is set, V implements T if all
279 // methods of T are present in V. Otherwise (V is an interface and static
280 // is not set), MissingMethod only checks that methods of T which are also
281 // present in V have matching types (e.g., for a type assertion x.(T) where
282 // x is of interface type V).
284 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
285 m, typ := (*Checker)(nil).missingMethod(V, T, static)
289 // missingMethod is like MissingMethod but accepts a *Checker as
290 // receiver and an addressable flag.
291 // The receiver may be nil if missingMethod is invoked through
292 // an exported API call (such as MissingMethod), i.e., when all
293 // methods have been type-checked.
294 // If the type has the correctly named method, but with the wrong
295 // signature, the existing method is returned as well.
296 // To improve error messages, also report the wrong signature
297 // when the method exists on *V instead of V.
298 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, wrongType *Func) {
299 // fast path for common case
304 if ityp := asInterface(V); ityp != nil {
305 // TODO(gri) the methods are sorted - could do this more efficiently
306 for _, m := range T.typeSet().methods {
307 _, f := ityp.typeSet().LookupMethod(m.pkg, m.name)
310 // if m is the magic method == we're ok (interfaces are comparable)
311 if m.name == "==" || !static {
317 // both methods must have the same number of type parameters
318 ftyp := f.typ.(*Signature)
319 mtyp := m.typ.(*Signature)
320 if ftyp.TParams().Len() != mtyp.TParams().Len() {
323 if ftyp.TParams().Len() > 0 {
324 panic("internal error: method with type parameters")
327 // If the methods have type parameters we don't care whether they
328 // are the same or not, as long as they match up. Use unification
329 // to see if they can be made to match.
330 // TODO(gri) is this always correct? what about type bounds?
331 // (Alternative is to rename/subst type parameters and compare.)
332 u := newUnifier(true)
333 u.x.init(ftyp.TParams().list())
334 if !u.unify(ftyp, mtyp) {
342 // A concrete type implements T if it implements all methods of T.
345 for _, m := range T.typeSet().methods {
346 // TODO(gri) should this be calling lookupFieldOrMethod instead (and why not)?
347 obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
349 // Check if *V implements this method of T.
352 obj, _, _ = lookupFieldOrMethod(ptr, false, m.pkg, m.name)
354 return m, obj.(*Func)
358 // we must have a method (not a field of matching function type)
361 // if m is the magic method == and V is comparable, we're ok
362 if m.name == "==" && Comparable(V) {
368 // methods may not have a fully set up signature yet
370 check.objDecl(f, nil)
373 // both methods must have the same number of type parameters
374 ftyp := f.typ.(*Signature)
375 mtyp := m.typ.(*Signature)
376 if ftyp.TParams().Len() != mtyp.TParams().Len() {
379 if ftyp.TParams().Len() > 0 {
380 panic("internal error: method with type parameters")
383 // If V is a (instantiated) generic type, its methods are still
384 // parameterized using the original (declaration) receiver type
385 // parameters (subst simply copies the existing method list, it
386 // does not instantiate the methods).
387 // In order to compare the signatures, substitute the receiver
388 // type parameters of ftyp with V's instantiation type arguments.
389 // This lazily instantiates the signature of method f.
390 if Vn != nil && Vn.TParams().Len() > 0 {
391 // Be careful: The number of type arguments may not match
392 // the number of receiver parameters. If so, an error was
393 // reported earlier but the length discrepancy is still
394 // here. Exit early in this case to prevent an assertion
395 // failure in makeSubstMap.
396 // TODO(gri) Can we avoid this check by fixing the lengths?
397 if len(ftyp.RParams().list()) != len(Vn.targs) {
400 ftyp = check.subst(token.NoPos, ftyp, makeSubstMap(ftyp.RParams().list(), Vn.targs)).(*Signature)
403 // If the methods have type parameters we don't care whether they
404 // are the same or not, as long as they match up. Use unification
405 // to see if they can be made to match.
406 // TODO(gri) is this always correct? what about type bounds?
407 // (Alternative is to rename/subst type parameters and compare.)
408 u := newUnifier(true)
409 u.x.init(ftyp.RParams().list())
410 if !u.unify(ftyp, mtyp) {
418 // assertableTo reports whether a value of type V can be asserted to have type T.
419 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing
420 // method required by V and whether it is missing or just has the wrong type.
421 // The receiver may be nil if assertableTo is invoked through an exported API call
422 // (such as AssertableTo), i.e., when all methods have been type-checked.
423 // If the global constant forceStrict is set, assertions that are known to fail
424 // are not permitted.
425 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
426 // no static check is required if T is an interface
427 // spec: "If T is an interface type, x.(T) asserts that the
428 // dynamic type of x implements the interface T."
429 if asInterface(T) != nil && !forceStrict {
432 return check.missingMethod(T, V, false)
435 // deref dereferences typ if it is a *Pointer and returns its base and true.
436 // Otherwise it returns (typ, false).
437 func deref(typ Type) (Type, bool) {
438 if p, _ := typ.(*Pointer); p != nil {
444 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
445 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
446 func derefStructPtr(typ Type) Type {
447 if p := asPointer(typ); p != nil {
448 if asStruct(p.base) != nil {
455 // concat returns the result of concatenating list and i.
456 // The result does not share its underlying array with list.
457 func concat(list []int, i int) []int {
459 t = append(t, list...)
463 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
464 func fieldIndex(fields []*Var, pkg *Package, name string) int {
466 for i, f := range fields {
467 if f.sameId(pkg, name) {
475 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
476 func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
478 for i, m := range methods {
479 if m.sameId(pkg, name) {