Source file src/go/types/selection.go

Documentation: go/types

     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.
     4  
     5  // This file implements Selections.
     6  
     7  package types
     8  
     9  import (
    10  	"bytes"
    11  	"fmt"
    12  )
    13  
    14  // SelectionKind describes the kind of a selector expression x.f
    15  // (excluding qualified identifiers).
    16  type SelectionKind int
    17  
    18  const (
    19  	FieldVal   SelectionKind = iota // x.f is a struct field selector
    20  	MethodVal                       // x.f is a method selector
    21  	MethodExpr                      // x.f is a method expression
    22  )
    23  
    24  // A Selection describes a selector expression x.f.
    25  // For the declarations:
    26  //
    27  //	type T struct{ x int; E }
    28  //	type E struct{}
    29  //	func (e E) m() {}
    30  //	var p *T
    31  //
    32  // the following relations exist:
    33  //
    34  //	Selector    Kind          Recv    Obj    Type               Index     Indirect
    35  //
    36  //	p.x         FieldVal      T       x      int                {0}       true
    37  //	p.m         MethodVal     *T      m      func (e *T) m()    {1, 0}    true
    38  //	T.m         MethodExpr    T       m      func m(_ T)        {1, 0}    false
    39  //
    40  type Selection struct {
    41  	kind     SelectionKind
    42  	recv     Type   // type of x
    43  	obj      Object // object denoted by x.f
    44  	index    []int  // path from x to x.f
    45  	indirect bool   // set if there was any pointer indirection on the path
    46  }
    47  
    48  // Kind returns the selection kind.
    49  func (s *Selection) Kind() SelectionKind { return s.kind }
    50  
    51  // Recv returns the type of x in x.f.
    52  func (s *Selection) Recv() Type { return s.recv }
    53  
    54  // Obj returns the object denoted by x.f; a *Var for
    55  // a field selection, and a *Func in all other cases.
    56  func (s *Selection) Obj() Object { return s.obj }
    57  
    58  // Type returns the type of x.f, which may be different from the type of f.
    59  // See Selection for more information.
    60  func (s *Selection) Type() Type {
    61  	switch s.kind {
    62  	case MethodVal:
    63  		// The type of x.f is a method with its receiver type set
    64  		// to the type of x.
    65  		sig := *s.obj.(*Func).typ.(*Signature)
    66  		recv := *sig.recv
    67  		recv.typ = s.recv
    68  		sig.recv = &recv
    69  		return &sig
    70  
    71  	case MethodExpr:
    72  		// The type of x.f is a function (without receiver)
    73  		// and an additional first argument with the same type as x.
    74  		// TODO(gri) Similar code is already in call.go - factor!
    75  		// TODO(gri) Compute this eagerly to avoid allocations.
    76  		sig := *s.obj.(*Func).typ.(*Signature)
    77  		arg0 := *sig.recv
    78  		sig.recv = nil
    79  		arg0.typ = s.recv
    80  		var params []*Var
    81  		if sig.params != nil {
    82  			params = sig.params.vars
    83  		}
    84  		sig.params = NewTuple(append([]*Var{&arg0}, params...)...)
    85  		return &sig
    86  	}
    87  
    88  	// In all other cases, the type of x.f is the type of x.
    89  	return s.obj.Type()
    90  }
    91  
    92  // Index describes the path from x to f in x.f.
    93  // The last index entry is the field or method index of the type declaring f;
    94  // either:
    95  //
    96  //	1) the list of declared methods of a named type; or
    97  //	2) the list of methods of an interface type; or
    98  //	3) the list of fields of a struct type.
    99  //
   100  // The earlier index entries are the indices of the embedded fields implicitly
   101  // traversed to get from (the type of) x to f, starting at embedding depth 0.
   102  func (s *Selection) Index() []int { return s.index }
   103  
   104  // Indirect reports whether any pointer indirection was required to get from
   105  // x to f in x.f.
   106  func (s *Selection) Indirect() bool { return s.indirect }
   107  
   108  func (s *Selection) String() string { return SelectionString(s, nil) }
   109  
   110  // SelectionString returns the string form of s.
   111  // The Qualifier controls the printing of
   112  // package-level objects, and may be nil.
   113  //
   114  // Examples:
   115  //	"field (T) f int"
   116  //	"method (T) f(X) Y"
   117  //	"method expr (T) f(X) Y"
   118  //
   119  func SelectionString(s *Selection, qf Qualifier) string {
   120  	var k string
   121  	switch s.kind {
   122  	case FieldVal:
   123  		k = "field "
   124  	case MethodVal:
   125  		k = "method "
   126  	case MethodExpr:
   127  		k = "method expr "
   128  	default:
   129  		unreachable()
   130  	}
   131  	var buf bytes.Buffer
   132  	buf.WriteString(k)
   133  	buf.WriteByte('(')
   134  	WriteType(&buf, s.Recv(), qf)
   135  	fmt.Fprintf(&buf, ") %s", s.obj.Name())
   136  	if T := s.Type(); s.kind == FieldVal {
   137  		buf.WriteByte(' ')
   138  		WriteType(&buf, T, qf)
   139  	} else {
   140  		WriteSignature(&buf, T.(*Signature), qf)
   141  	}
   142  	return buf.String()
   143  }
   144  

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