// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file implements various field and method lookup functions.
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package types
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// Internal use of LookupFieldOrMethod: If the obj result is a method
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// associated with a concrete (non-interface) type, the method's signature
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// may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
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// the method's type.
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// LookupFieldOrMethod looks up a field or method with given package and name
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// in T and returns the corresponding *Var or *Func, an index sequence, and a
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// bool indicating if there were any pointer indirections on the path to the
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// field or method. If addressable is set, T is the type of an addressable
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// variable (only matters for method lookups).
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//
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// The last index entry is the field or method index in the (possibly embedded)
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// type where the entry was found, either:
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//
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// 1) the list of declared methods of a named type; or
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// 2) the list of all methods (method set) of an interface type; or
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// 3) the list of fields of a struct type.
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//
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// The earlier index entries are the indices of the embedded struct fields
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// traversed to get to the found entry, starting at depth 0.
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//
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// If no entry is found, a nil object is returned. In this case, the returned
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// index and indirect values have the following meaning:
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//
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// - If index != nil, the index sequence points to an ambiguous entry
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// (the same name appeared more than once at the same embedding level).
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//
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// - If indirect is set, a method with a pointer receiver type was found
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// but there was no pointer on the path from the actual receiver type to
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// the method's formal receiver base type, nor was the receiver addressable.
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//
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func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
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// Methods cannot be associated to a named pointer type
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// (spec: "The type denoted by T is called the receiver base type;
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// it must not be a pointer or interface type and it must be declared
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// in the same package as the method.").
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// Thus, if we have a named pointer type, proceed with the underlying
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// pointer type but discard the result if it is a method since we would
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// not have found it for T (see also issue 8590).
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if t, _ := T.(*Named); t != nil {
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if p, _ := t.underlying.(*Pointer); p != nil {
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obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
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if _, ok := obj.(*Func); ok {
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return nil, nil, false
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}
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return
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}
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}
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return lookupFieldOrMethod(T, addressable, pkg, name)
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}
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// TODO(gri) The named type consolidation and seen maps below must be
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// indexed by unique keys for a given type. Verify that named
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// types always have only one representation (even when imported
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// indirectly via different packages.)
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func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
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// WARNING: The code in this function is extremely subtle - do not modify casually!
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// This function and NewMethodSet should be kept in sync.
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if name == "_" {
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return // blank fields/methods are never found
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}
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typ, isPtr := deref(T)
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// *typ where typ is an interface has no methods.
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if isPtr && IsInterface(typ) {
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return
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}
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// Start with typ as single entry at shallowest depth.
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current := []embeddedType{{typ, nil, isPtr, false}}
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// Named types that we have seen already, allocated lazily.
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// Used to avoid endless searches in case of recursive types.
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// Since only Named types can be used for recursive types, we
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// only need to track those.
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// (If we ever allow type aliases to construct recursive types,
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// we must use type identity rather than pointer equality for
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// the map key comparison, as we do in consolidateMultiples.)
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var seen map[*Named]bool
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// search current depth
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for len(current) > 0 {
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var next []embeddedType // embedded types found at current depth
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// look for (pkg, name) in all types at current depth
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for _, e := range current {
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typ := e.typ
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// If we have a named type, we may have associated methods.
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// Look for those first.
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if named, _ := typ.(*Named); named != nil {
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if seen[named] {
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// We have seen this type before, at a more shallow depth
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// (note that multiples of this type at the current depth
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// were consolidated before). The type at that depth shadows
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// this same type at the current depth, so we can ignore
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// this one.
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continue
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}
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if seen == nil {
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seen = make(map[*Named]bool)
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}
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seen[named] = true
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// look for a matching attached method
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if i, m := lookupMethod(named.methods, pkg, name); m != nil {
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// potential match
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// caution: method may not have a proper signature yet
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index = concat(e.index, i)
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if obj != nil || e.multiples {
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return nil, index, false // collision
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}
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obj = m
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indirect = e.indirect
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continue // we can't have a matching field or interface method
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}
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// continue with underlying type
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typ = named.underlying
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}
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switch t := typ.(type) {
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case *Struct:
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// look for a matching field and collect embedded types
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for i, f := range t.fields {
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if f.sameId(pkg, name) {
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assert(f.typ != nil)
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index = concat(e.index, i)
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if obj != nil || e.multiples {
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return nil, index, false // collision
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}
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obj = f
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indirect = e.indirect
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continue // we can't have a matching interface method
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}
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// Collect embedded struct fields for searching the next
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// lower depth, but only if we have not seen a match yet
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// (if we have a match it is either the desired field or
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// we have a name collision on the same depth; in either
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// case we don't need to look further).
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// Embedded fields are always of the form T or *T where
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// T is a type name. If e.typ appeared multiple times at
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// this depth, f.typ appears multiple times at the next
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// depth.
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if obj == nil && f.embedded {
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typ, isPtr := deref(f.typ)
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// TODO(gri) optimization: ignore types that can't
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// have fields or methods (only Named, Struct, and
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// Interface types need to be considered).
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next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
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}
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}
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case *Interface:
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// look for a matching method
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// TODO(gri) t.allMethods is sorted - use binary search
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if i, m := lookupMethod(t.allMethods, pkg, name); m != nil {
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assert(m.typ != nil)
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index = concat(e.index, i)
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if obj != nil || e.multiples {
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return nil, index, false // collision
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}
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obj = m
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indirect = e.indirect
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}
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}
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}
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if obj != nil {
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// found a potential match
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// spec: "A method call x.m() is valid if the method set of (the type of) x
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// contains m and the argument list can be assigned to the parameter
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// list of m. If x is addressable and &x's method set contains m, x.m()
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// is shorthand for (&x).m()".
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if f, _ := obj.(*Func); f != nil && ptrRecv(f) && !indirect && !addressable {
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return nil, nil, true // pointer/addressable receiver required
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}
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return
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}
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current = consolidateMultiples(next)
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}
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return nil, nil, false // not found
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}
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// embeddedType represents an embedded type
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type embeddedType struct {
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typ Type
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index []int // embedded field indices, starting with index at depth 0
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indirect bool // if set, there was a pointer indirection on the path to this field
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multiples bool // if set, typ appears multiple times at this depth
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}
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// consolidateMultiples collects multiple list entries with the same type
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// into a single entry marked as containing multiples. The result is the
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// consolidated list.
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func consolidateMultiples(list []embeddedType) []embeddedType {
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if len(list) <= 1 {
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return list // at most one entry - nothing to do
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}
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n := 0 // number of entries w/ unique type
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prev := make(map[Type]int) // index at which type was previously seen
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for _, e := range list {
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if i, found := lookupType(prev, e.typ); found {
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list[i].multiples = true
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// ignore this entry
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} else {
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prev[e.typ] = n
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list[n] = e
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n++
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}
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}
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return list[:n]
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}
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func lookupType(m map[Type]int, typ Type) (int, bool) {
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// fast path: maybe the types are equal
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if i, found := m[typ]; found {
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return i, true
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}
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for t, i := range m {
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if Identical(t, typ) {
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return i, true
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}
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}
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return 0, false
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}
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// MissingMethod returns (nil, false) if V implements T, otherwise it
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// returns a missing method required by T and whether it is missing or
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// just has the wrong type.
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//
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// For non-interface types V, or if static is set, V implements T if all
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// methods of T are present in V. Otherwise (V is an interface and static
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// is not set), MissingMethod only checks that methods of T which are also
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// present in V have matching types (e.g., for a type assertion x.(T) where
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// x is of interface type V).
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//
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func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
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return (*Checker)(nil).missingMethod(V, T, static)
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}
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// missingMethod is like MissingMethod but accepts a receiver.
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// The receiver may be nil if missingMethod is invoked through
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// an exported API call (such as MissingMethod), i.e., when all
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// methods have been type-checked.
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func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
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// fast path for common case
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if T.Empty() {
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return
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}
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// TODO(gri) Consider using method sets here. Might be more efficient.
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if ityp, _ := V.Underlying().(*Interface); ityp != nil {
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// TODO(gri) allMethods is sorted - can do this more efficiently
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for _, m := range T.allMethods {
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_, obj := lookupMethod(ityp.allMethods, m.pkg, m.name)
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switch {
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case obj == nil:
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if static {
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return m, false
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}
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case !Identical(obj.Type(), m.typ):
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return m, true
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}
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}
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return
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}
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// A concrete type implements T if it implements all methods of T.
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for _, m := range T.allMethods {
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obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
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// we must have a method (not a field of matching function type)
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f, _ := obj.(*Func)
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if f == nil {
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return m, false
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}
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// methods may not have a fully set up signature yet
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if check != nil {
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check.objDecl(f, nil)
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}
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if !Identical(f.typ, m.typ) {
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return m, true
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}
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}
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return
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}
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// assertableTo reports whether a value of type V can be asserted to have type T.
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// It returns (nil, false) as affirmative answer. Otherwise it returns a missing
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// method required by V and whether it is missing or just has the wrong type.
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// The receiver may be nil if assertableTo is invoked through an exported API call
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// (such as AssertableTo), i.e., when all methods have been type-checked.
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func (check *Checker) assertableTo(V *Interface, T Type) (method *Func, wrongType bool) {
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// no static check is required if T is an interface
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// spec: "If T is an interface type, x.(T) asserts that the
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// dynamic type of x implements the interface T."
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if _, ok := T.Underlying().(*Interface); ok && !strict {
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return
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}
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return check.missingMethod(T, V, false)
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}
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// deref dereferences typ if it is a *Pointer and returns its base and true.
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// Otherwise it returns (typ, false).
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func deref(typ Type) (Type, bool) {
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if p, _ := typ.(*Pointer); p != nil {
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return p.base, true
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}
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return typ, false
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}
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// derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
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// (named or unnamed) struct and returns its base. Otherwise it returns typ.
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func derefStructPtr(typ Type) Type {
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if p, _ := typ.Underlying().(*Pointer); p != nil {
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if _, ok := p.base.Underlying().(*Struct); ok {
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return p.base
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}
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}
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return typ
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}
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// concat returns the result of concatenating list and i.
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// The result does not share its underlying array with list.
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func concat(list []int, i int) []int {
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var t []int
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t = append(t, list...)
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return append(t, i)
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}
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// fieldIndex returns the index for the field with matching package and name, or a value < 0.
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func fieldIndex(fields []*Var, pkg *Package, name string) int {
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if name != "_" {
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for i, f := range fields {
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if f.sameId(pkg, name) {
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return i
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}
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}
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}
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return -1
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}
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// lookupMethod returns the index of and method with matching package and name, or (-1, nil).
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func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
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if name != "_" {
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for i, m := range methods {
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if m.sameId(pkg, name) {
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return i, m
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}
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}
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}
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return -1, nil
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}
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