go lookup 源码
golang lookup 代码
文件路径：/src/cmd/compile/internal/types2/lookup.go
// Copyright 2013 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 various field and method lookup functions.
package types2
import (
"bytes"
"strings"
)
// Internal use of LookupFieldOrMethod: If the obj result is a method
// associated with a concrete (non-interface) type, the method's signature
// may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
// the method's type.
// LookupFieldOrMethod looks up a field or method with given package and name
// in T and returns the corresponding *Var or *Func, an index sequence, and a
// bool indicating if there were any pointer indirections on the path to the
// field or method. If addressable is set, T is the type of an addressable
// variable (only matters for method lookups). T must not be nil.
//
// The last index entry is the field or method index in the (possibly embedded)
// type where the entry was found, either:
//
// 1. the list of declared methods of a named type; or
// 2. the list of all methods (method set) of an interface type; or
// 3. the list of fields of a struct type.
//
// The earlier index entries are the indices of the embedded struct fields
// traversed to get to the found entry, starting at depth 0.
//
// If no entry is found, a nil object is returned. In this case, the returned
// index and indirect values have the following meaning:
//
// - If index != nil, the index sequence points to an ambiguous entry
// (the same name appeared more than once at the same embedding level).
//
// - If indirect is set, a method with a pointer receiver type was found
// but there was no pointer on the path from the actual receiver type to
// the method's formal receiver base type, nor was the receiver addressable.
func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
if T == nil {
panic("LookupFieldOrMethod on nil type")
}
// Methods cannot be associated to a named pointer type.
// (spec: "The type denoted by T is called the receiver base type;
// it must not be a pointer or interface type and it must be declared
// in the same package as the method.").
// Thus, if we have a named pointer type, proceed with the underlying
// pointer type but discard the result if it is a method since we would
// not have found it for T (see also issue 8590).
if t, _ := T.(*Named); t != nil {
if p, _ := t.Underlying().(*Pointer); p != nil {
obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name, false)
if _, ok := obj.(*Func); ok {
return nil, nil, false
}
return
}
}
obj, index, indirect = lookupFieldOrMethod(T, addressable, pkg, name, false)
// If we didn't find anything and if we have a type parameter with a core type,
// see if there is a matching field (but not a method, those need to be declared
// explicitly in the constraint). If the constraint is a named pointer type (see
// above), we are ok here because only fields are accepted as results.
const enableTParamFieldLookup = false // see issue #51576
if enableTParamFieldLookup && obj == nil && isTypeParam(T) {
if t := coreType(T); t != nil {
obj, index, indirect = lookupFieldOrMethod(t, addressable, pkg, name, false)
if _, ok := obj.(*Var); !ok {
obj, index, indirect = nil, nil, false // accept fields (variables) only
}
}
}
return
}
// lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
// If foldCase is true, the lookup for methods will include looking for any method
// which case-folds to the same as 'name' (used for giving helpful error messages).
//
// The resulting object may not be fully type-checked.
func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, foldCase bool) (obj Object, index []int, indirect bool) {
// WARNING: The code in this function is extremely subtle - do not modify casually!
if name == "_" {
return // blank fields/methods are never found
}
typ, isPtr := deref(T)
// *typ where typ is an interface (incl. a type parameter) has no methods.
if isPtr {
if _, ok := under(typ).(*Interface); ok {
return
}
}
// Start with typ as single entry at shallowest depth.
current := []embeddedType{{typ, nil, isPtr, false}}
// seen tracks named types that we have seen already, allocated lazily.
// Used to avoid endless searches in case of recursive types.
//
// We must use a lookup on identity rather than a simple map[*Named]bool as
// instantiated types may be identical but not equal.
var seen instanceLookup
// search current depth
for len(current) > 0 {
var next []embeddedType // embedded types found at current depth
// look for (pkg, name) in all types at current depth
for _, e := range current {
typ := e.typ
// If we have a named type, we may have associated methods.
// Look for those first.
if named, _ := typ.(*Named); named != nil {
if alt := seen.lookup(named); alt != nil {
// We have seen this type before, at a more shallow depth
// (note that multiples of this type at the current depth
// were consolidated before). The type at that depth shadows
// this same type at the current depth, so we can ignore
// this one.
continue
}
seen.add(named)
// look for a matching attached method
if i, m := named.lookupMethod(pkg, name, foldCase); m != nil {
// potential match
// caution: method may not have a proper signature yet
index = concat(e.index, i)
if obj != nil || e.multiples {
return nil, index, false // collision
}
obj = m
indirect = e.indirect
continue // we can't have a matching field or interface method
}
}
switch t := under(typ).(type) {
case *Struct:
// look for a matching field and collect embedded types
for i, f := range t.fields {
if f.sameId(pkg, name) {
assert(f.typ != nil)
index = concat(e.index, i)
if obj != nil || e.multiples {
return nil, index, false // collision
}
obj = f
indirect = e.indirect
continue // we can't have a matching interface method
}
// Collect embedded struct fields for searching the next
// lower depth, but only if we have not seen a match yet
// (if we have a match it is either the desired field or
// we have a name collision on the same depth; in either
// case we don't need to look further).
// Embedded fields are always of the form T or *T where
// T is a type name. If e.typ appeared multiple times at
// this depth, f.typ appears multiple times at the next
// depth.
if obj == nil && f.embedded {
typ, isPtr := deref(f.typ)
// TODO(gri) optimization: ignore types that can't
// have fields or methods (only Named, Struct, and
// Interface types need to be considered).
next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
}
}
case *Interface:
// look for a matching method (interface may be a type parameter)
if i, m := t.typeSet().LookupMethod(pkg, name, foldCase); m != nil {
assert(m.typ != nil)
index = concat(e.index, i)
if obj != nil || e.multiples {
return nil, index, false // collision
}
obj = m
indirect = e.indirect
}
}
}
if obj != nil {
// found a potential match
// spec: "A method call x.m() is valid if the method set of (the type of) x
// contains m and the argument list can be assigned to the parameter
// list of m. If x is addressable and &x's method set contains m, x.m()
// is shorthand for (&x).m()".
if f, _ := obj.(*Func); f != nil {
// determine if method has a pointer receiver
if f.hasPtrRecv() && !indirect && !addressable {
return nil, nil, true // pointer/addressable receiver required
}
}
return
}
current = consolidateMultiples(next)
}
return nil, nil, false // not found
}
// embeddedType represents an embedded type
type embeddedType struct {
typ Type
index []int // embedded field indices, starting with index at depth 0
indirect bool // if set, there was a pointer indirection on the path to this field
multiples bool // if set, typ appears multiple times at this depth
}
// consolidateMultiples collects multiple list entries with the same type
// into a single entry marked as containing multiples. The result is the
// consolidated list.
func consolidateMultiples(list []embeddedType) []embeddedType {
if len(list) <= 1 {
return list // at most one entry - nothing to do
}
n := 0 // number of entries w/ unique type
prev := make(map[Type]int) // index at which type was previously seen
for _, e := range list {
if i, found := lookupType(prev, e.typ); found {
list[i].multiples = true
// ignore this entry
} else {
prev[e.typ] = n
list[n] = e
n++
}
}
return list[:n]
}
func lookupType(m map[Type]int, typ Type) (int, bool) {
// fast path: maybe the types are equal
if i, found := m[typ]; found {
return i, true
}
for t, i := range m {
if Identical(t, typ) {
return i, true
}
}
return 0, false
}
type instanceLookup struct {
m map[*Named][]*Named
}
func (l *instanceLookup) lookup(inst *Named) *Named {
for _, t := range l.m[inst.Origin()] {
if Identical(inst, t) {
return t
}
}
return nil
}
func (l *instanceLookup) add(inst *Named) {
if l.m == nil {
l.m = make(map[*Named][]*Named)
}
insts := l.m[inst.Origin()]
l.m[inst.Origin()] = append(insts, inst)
}
// MissingMethod returns (nil, false) if V implements T, otherwise it
// returns a missing method required by T and whether it is missing or
// just has the wrong type.
//
// For non-interface types V, or if static is set, V implements T if all
// methods of T are present in V. Otherwise (V is an interface and static
// is not set), MissingMethod only checks that methods of T which are also
// present in V have matching types (e.g., for a type assertion x.(T) where
// x is of interface type V).
func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
m, alt := (*Checker)(nil).missingMethod(V, T, static)
// Only report a wrong type if the alternative method has the same name as m.
return m, alt != nil && alt.name == m.name // alt != nil implies m != nil
}
// missingMethod is like MissingMethod but accepts a *Checker as receiver.
// The receiver may be nil if missingMethod is invoked through an exported
// API call (such as MissingMethod), i.e., when all methods have been type-
// checked.
//
// If a method is missing on T but is found on *T, or if a method is found
// on T when looked up with case-folding, this alternative method is returned
// as the second result.
func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, alt *Func) {
if T.NumMethods() == 0 {
return
}
// V is an interface
if u, _ := under(V).(*Interface); u != nil {
tset := u.typeSet()
for _, m := range T.typeSet().methods {
_, f := tset.LookupMethod(m.pkg, m.name, false)
if f == nil {
if !static {
continue
}
return m, nil
}
if !Identical(f.typ, m.typ) {
return m, f
}
}
return
}
// V is not an interface
for _, m := range T.typeSet().methods {
// TODO(gri) should this be calling LookupFieldOrMethod instead (and why not)?
obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name, false)
// check if m is on *V, or on V with case-folding
found := obj != nil
if !found {
// TODO(gri) Instead of NewPointer(V) below, can we just set the "addressable" argument?
obj, _, _ = lookupFieldOrMethod(NewPointer(V), false, m.pkg, m.name, false)
if obj == nil {
obj, _, _ = lookupFieldOrMethod(V, false, m.pkg, m.name, true /* fold case */)
}
}
// we must have a method (not a struct field)
f, _ := obj.(*Func)
if f == nil {
return m, nil
}
// methods may not have a fully set up signature yet
if check != nil {
check.objDecl(f, nil)
}
if !found || !Identical(f.typ, m.typ) {
return m, f
}
}
return
}
// missingMethodReason returns a string giving the detailed reason for a missing method m,
// where m is missing from V, but required by T. It puts the reason in parentheses,
// and may include more have/want info after that. If non-nil, alt is a relevant
// method that matches in some way. It may have the correct name, but wrong type, or
// it may have a pointer receiver, or it may have the correct name except wrong case.
// check may be nil.
func (check *Checker) missingMethodReason(V, T Type, m, alt *Func) string {
var mname string
if check != nil && check.conf.CompilerErrorMessages {
mname = m.Name() + " method"
} else {
mname = "method " + m.Name()
}
if alt != nil {
if m.Name() != alt.Name() {
return check.sprintf("(missing %s)\n\t\thave %s\n\t\twant %s",
mname, check.funcString(alt), check.funcString(m))
}
if Identical(m.typ, alt.typ) {
return check.sprintf("(%s has pointer receiver)", mname)
}
return check.sprintf("(wrong type for %s)\n\t\thave %s\n\t\twant %s",
mname, check.funcString(alt), check.funcString(m))
}
if isInterfacePtr(V) {
return "(" + check.interfacePtrError(V) + ")"
}
if isInterfacePtr(T) {
return "(" + check.interfacePtrError(T) + ")"
}
return check.sprintf("(missing %s)", mname)
}
func isInterfacePtr(T Type) bool {
p, _ := under(T).(*Pointer)
return p != nil && IsInterface(p.base)
}
// check may be nil.
func (check *Checker) interfacePtrError(T Type) string {
assert(isInterfacePtr(T))
if p, _ := under(T).(*Pointer); isTypeParam(p.base) {
return check.sprintf("type %s is pointer to type parameter, not type parameter", T)
}
return check.sprintf("type %s is pointer to interface, not interface", T)
}
// funcString returns a string of the form name + signature for f.
// check may be nil.
func (check *Checker) funcString(f *Func) string {
buf := bytes.NewBufferString(f.name)
var qf Qualifier
if check != nil {
qf = check.qualifier
}
WriteSignature(buf, f.typ.(*Signature), qf)
return buf.String()
}
// assertableTo reports whether a value of type V can be asserted to have type T.
// It returns (nil, false) as affirmative answer. Otherwise it returns a missing
// method required by V and whether it is missing or just has the wrong type.
// The receiver may be nil if assertableTo is invoked through an exported API call
// (such as AssertableTo), i.e., when all methods have been type-checked.
// TODO(gri) replace calls to this function with calls to newAssertableTo.
func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
// no static check is required if T is an interface
// spec: "If T is an interface type, x.(T) asserts that the
// dynamic type of x implements the interface T."
if IsInterface(T) {
return
}
// TODO(gri) fix this for generalized interfaces
return check.missingMethod(T, V, false)
}
// newAssertableTo reports whether a value of type V can be asserted to have type T.
// It also implements behavior for interfaces that currently are only permitted
// in constraint position (we have not yet defined that behavior in the spec).
func (check *Checker) newAssertableTo(V *Interface, T Type) error {
// no static check is required if T is an interface
// spec: "If T is an interface type, x.(T) asserts that the
// dynamic type of x implements the interface T."
if IsInterface(T) {
return nil
}
return check.implements(T, V)
}
// deref dereferences typ if it is a *Pointer and returns its base and true.
// Otherwise it returns (typ, false).
func deref(typ Type) (Type, bool) {
if p, _ := typ.(*Pointer); p != nil {
// p.base should never be nil, but be conservative
if p.base == nil {
if debug {
panic("pointer with nil base type (possibly due to an invalid cyclic declaration)")
}
return Typ[Invalid], true
}
return p.base, true
}
return typ, false
}
// derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
// (named or unnamed) struct and returns its base. Otherwise it returns typ.
func derefStructPtr(typ Type) Type {
if p, _ := under(typ).(*Pointer); p != nil {
if _, ok := under(p.base).(*Struct); ok {
return p.base
}
}
return typ
}
// concat returns the result of concatenating list and i.
// The result does not share its underlying array with list.
func concat(list []int, i int) []int {
var t []int
t = append(t, list...)
return append(t, i)
}
// fieldIndex returns the index for the field with matching package and name, or a value < 0.
func fieldIndex(fields []*Var, pkg *Package, name string) int {
if name != "_" {
for i, f := range fields {
if f.sameId(pkg, name) {
return i
}
}
}
return -1
}
// lookupMethod returns the index of and method with matching package and name, or (-1, nil).
// If foldCase is true, method names are considered equal if they are equal with case folding.
func lookupMethod(methods []*Func, pkg *Package, name string, foldCase bool) (int, *Func) {
if name != "_" {
for i, m := range methods {
if (m.name == name || foldCase && strings.EqualFold(m.name, name)) && m.sameId(pkg, m.name) {
return i, m
}
}
}
return -1, nil
}
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