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Source file src/go/types/object.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  package types
     6  
     7  import (
     8  	"bytes"
     9  	"fmt"
    10  	"go/constant"
    11  	"go/token"
    12  )
    13  
    14  // An Object describes a named language entity such as a package,
    15  // constant, type, variable, function (incl. methods), or label.
    16  // All objects implement the Object interface.
    17  //
    18  type Object interface {
    19  	Parent() *Scope // scope in which this object is declared; nil for methods and struct fields
    20  	Pos() token.Pos // position of object identifier in declaration
    21  	Pkg() *Package  // package to which this object belongs; nil for labels and objects in the Universe scope
    22  	Name() string   // package local object name
    23  	Type() Type     // object type
    24  	Exported() bool // reports whether the name starts with a capital letter
    25  	Id() string     // object name if exported, qualified name if not exported (see func Id)
    26  
    27  	// String returns a human-readable string of the object.
    28  	String() string
    29  
    30  	// order reflects a package-level object's source order: if object
    31  	// a is before object b in the source, then a.order() < b.order().
    32  	// order returns a value > 0 for package-level objects; it returns
    33  	// 0 for all other objects (including objects in file scopes).
    34  	order() uint32
    35  
    36  	// color returns the object's color.
    37  	color() color
    38  
    39  	// setType sets the type of the object.
    40  	setType(Type)
    41  
    42  	// setOrder sets the order number of the object. It must be > 0.
    43  	setOrder(uint32)
    44  
    45  	// setColor sets the object's color. It must not be white.
    46  	setColor(color color)
    47  
    48  	// setParent sets the parent scope of the object.
    49  	setParent(*Scope)
    50  
    51  	// sameId reports whether obj.Id() and Id(pkg, name) are the same.
    52  	sameId(pkg *Package, name string) bool
    53  
    54  	// scopePos returns the start position of the scope of this Object
    55  	scopePos() token.Pos
    56  
    57  	// setScopePos sets the start position of the scope for this Object.
    58  	setScopePos(pos token.Pos)
    59  }
    60  
    61  // Id returns name if it is exported, otherwise it
    62  // returns the name qualified with the package path.
    63  func Id(pkg *Package, name string) string {
    64  	if token.IsExported(name) {
    65  		return name
    66  	}
    67  	// unexported names need the package path for differentiation
    68  	// (if there's no package, make sure we don't start with '.'
    69  	// as that may change the order of methods between a setup
    70  	// inside a package and outside a package - which breaks some
    71  	// tests)
    72  	path := "_"
    73  	// pkg is nil for objects in Universe scope and possibly types
    74  	// introduced via Eval (see also comment in object.sameId)
    75  	if pkg != nil && pkg.path != "" {
    76  		path = pkg.path
    77  	}
    78  	return path + "." + name
    79  }
    80  
    81  // An object implements the common parts of an Object.
    82  type object struct {
    83  	parent    *Scope
    84  	pos       token.Pos
    85  	pkg       *Package
    86  	name      string
    87  	typ       Type
    88  	order_    uint32
    89  	color_    color
    90  	scopePos_ token.Pos
    91  }
    92  
    93  // color encodes the color of an object (see Checker.objDecl for details).
    94  type color uint32
    95  
    96  // An object may be painted in one of three colors.
    97  // Color values other than white or black are considered grey.
    98  const (
    99  	white color = iota
   100  	black
   101  	grey // must be > white and black
   102  )
   103  
   104  func (c color) String() string {
   105  	switch c {
   106  	case white:
   107  		return "white"
   108  	case black:
   109  		return "black"
   110  	default:
   111  		return "grey"
   112  	}
   113  }
   114  
   115  // colorFor returns the (initial) color for an object depending on
   116  // whether its type t is known or not.
   117  func colorFor(t Type) color {
   118  	if t != nil {
   119  		return black
   120  	}
   121  	return white
   122  }
   123  
   124  // Parent returns the scope in which the object is declared.
   125  // The result is nil for methods and struct fields.
   126  func (obj *object) Parent() *Scope { return obj.parent }
   127  
   128  // Pos returns the declaration position of the object's identifier.
   129  func (obj *object) Pos() token.Pos { return obj.pos }
   130  
   131  // Pkg returns the package to which the object belongs.
   132  // The result is nil for labels and objects in the Universe scope.
   133  func (obj *object) Pkg() *Package { return obj.pkg }
   134  
   135  // Name returns the object's (package-local, unqualified) name.
   136  func (obj *object) Name() string { return obj.name }
   137  
   138  // Type returns the object's type.
   139  func (obj *object) Type() Type { return obj.typ }
   140  
   141  // Exported reports whether the object is exported (starts with a capital letter).
   142  // It doesn't take into account whether the object is in a local (function) scope
   143  // or not.
   144  func (obj *object) Exported() bool { return token.IsExported(obj.name) }
   145  
   146  // Id is a wrapper for Id(obj.Pkg(), obj.Name()).
   147  func (obj *object) Id() string { return Id(obj.pkg, obj.name) }
   148  
   149  func (obj *object) String() string      { panic("abstract") }
   150  func (obj *object) order() uint32       { return obj.order_ }
   151  func (obj *object) color() color        { return obj.color_ }
   152  func (obj *object) scopePos() token.Pos { return obj.scopePos_ }
   153  
   154  func (obj *object) setParent(parent *Scope)   { obj.parent = parent }
   155  func (obj *object) setType(typ Type)          { obj.typ = typ }
   156  func (obj *object) setOrder(order uint32)     { assert(order > 0); obj.order_ = order }
   157  func (obj *object) setColor(color color)      { assert(color != white); obj.color_ = color }
   158  func (obj *object) setScopePos(pos token.Pos) { obj.scopePos_ = pos }
   159  
   160  func (obj *object) sameId(pkg *Package, name string) bool {
   161  	// spec:
   162  	// "Two identifiers are different if they are spelled differently,
   163  	// or if they appear in different packages and are not exported.
   164  	// Otherwise, they are the same."
   165  	if name != obj.name {
   166  		return false
   167  	}
   168  	// obj.Name == name
   169  	if obj.Exported() {
   170  		return true
   171  	}
   172  	// not exported, so packages must be the same (pkg == nil for
   173  	// fields in Universe scope; this can only happen for types
   174  	// introduced via Eval)
   175  	if pkg == nil || obj.pkg == nil {
   176  		return pkg == obj.pkg
   177  	}
   178  	// pkg != nil && obj.pkg != nil
   179  	return pkg.path == obj.pkg.path
   180  }
   181  
   182  // A PkgName represents an imported Go package.
   183  // PkgNames don't have a type.
   184  type PkgName struct {
   185  	object
   186  	imported *Package
   187  	used     bool // set if the package was used
   188  }
   189  
   190  // NewPkgName returns a new PkgName object representing an imported package.
   191  // The remaining arguments set the attributes found with all Objects.
   192  func NewPkgName(pos token.Pos, pkg *Package, name string, imported *Package) *PkgName {
   193  	return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, token.NoPos}, imported, false}
   194  }
   195  
   196  // Imported returns the package that was imported.
   197  // It is distinct from Pkg(), which is the package containing the import statement.
   198  func (obj *PkgName) Imported() *Package { return obj.imported }
   199  
   200  // A Const represents a declared constant.
   201  type Const struct {
   202  	object
   203  	val constant.Value
   204  }
   205  
   206  // NewConst returns a new constant with value val.
   207  // The remaining arguments set the attributes found with all Objects.
   208  func NewConst(pos token.Pos, pkg *Package, name string, typ Type, val constant.Value) *Const {
   209  	return &Const{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, val}
   210  }
   211  
   212  // Val returns the constant's value.
   213  func (obj *Const) Val() constant.Value { return obj.val }
   214  
   215  func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
   216  
   217  // A TypeName represents a name for a (defined or alias) type.
   218  type TypeName struct {
   219  	object
   220  }
   221  
   222  // NewTypeName returns a new type name denoting the given typ.
   223  // The remaining arguments set the attributes found with all Objects.
   224  //
   225  // The typ argument may be a defined (Named) type or an alias type.
   226  // It may also be nil such that the returned TypeName can be used as
   227  // argument for NewNamed, which will set the TypeName's type as a side-
   228  // effect.
   229  func NewTypeName(pos token.Pos, pkg *Package, name string, typ Type) *TypeName {
   230  	return &TypeName{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
   231  }
   232  
   233  // IsAlias reports whether obj is an alias name for a type.
   234  func (obj *TypeName) IsAlias() bool {
   235  	switch t := obj.typ.(type) {
   236  	case nil:
   237  		return false
   238  	case *Basic:
   239  		// unsafe.Pointer is not an alias.
   240  		if obj.pkg == Unsafe {
   241  			return false
   242  		}
   243  		// Any user-defined type name for a basic type is an alias for a
   244  		// basic type (because basic types are pre-declared in the Universe
   245  		// scope, outside any package scope), and so is any type name with
   246  		// a different name than the name of the basic type it refers to.
   247  		// Additionally, we need to look for "byte" and "rune" because they
   248  		// are aliases but have the same names (for better error messages).
   249  		return obj.pkg != nil || t.name != obj.name || t == universeByte || t == universeRune
   250  	case *Named:
   251  		return obj != t.obj
   252  	default:
   253  		return true
   254  	}
   255  }
   256  
   257  // A Variable represents a declared variable (including function parameters and results, and struct fields).
   258  type Var struct {
   259  	object
   260  	embedded bool // if set, the variable is an embedded struct field, and name is the type name
   261  	isField  bool // var is struct field
   262  	used     bool // set if the variable was used
   263  }
   264  
   265  // NewVar returns a new variable.
   266  // The arguments set the attributes found with all Objects.
   267  func NewVar(pos token.Pos, pkg *Package, name string, typ Type) *Var {
   268  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
   269  }
   270  
   271  // NewParam returns a new variable representing a function parameter.
   272  func NewParam(pos token.Pos, pkg *Package, name string, typ Type) *Var {
   273  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, used: true} // parameters are always 'used'
   274  }
   275  
   276  // NewField returns a new variable representing a struct field.
   277  // For embedded fields, the name is the unqualified type name
   278  /// under which the field is accessible.
   279  func NewField(pos token.Pos, pkg *Package, name string, typ Type, embedded bool) *Var {
   280  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, embedded: embedded, isField: true}
   281  }
   282  
   283  // Anonymous reports whether the variable is an embedded field.
   284  // Same as Embedded; only present for backward-compatibility.
   285  func (obj *Var) Anonymous() bool { return obj.embedded }
   286  
   287  // Embedded reports whether the variable is an embedded field.
   288  func (obj *Var) Embedded() bool { return obj.embedded }
   289  
   290  // IsField reports whether the variable is a struct field.
   291  func (obj *Var) IsField() bool { return obj.isField }
   292  
   293  func (*Var) isDependency() {} // a variable may be a dependency of an initialization expression
   294  
   295  // A Func represents a declared function, concrete method, or abstract
   296  // (interface) method. Its Type() is always a *Signature.
   297  // An abstract method may belong to many interfaces due to embedding.
   298  type Func struct {
   299  	object
   300  	hasPtrRecv bool // only valid for methods that don't have a type yet
   301  }
   302  
   303  // NewFunc returns a new function with the given signature, representing
   304  // the function's type.
   305  func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
   306  	// don't store a (typed) nil signature
   307  	var typ Type
   308  	if sig != nil {
   309  		typ = sig
   310  	}
   311  	return &Func{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, false}
   312  }
   313  
   314  // FullName returns the package- or receiver-type-qualified name of
   315  // function or method obj.
   316  func (obj *Func) FullName() string {
   317  	var buf bytes.Buffer
   318  	writeFuncName(&buf, obj, nil)
   319  	return buf.String()
   320  }
   321  
   322  // Scope returns the scope of the function's body block.
   323  func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
   324  
   325  func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
   326  
   327  // A Label represents a declared label.
   328  // Labels don't have a type.
   329  type Label struct {
   330  	object
   331  	used bool // set if the label was used
   332  }
   333  
   334  // NewLabel returns a new label.
   335  func NewLabel(pos token.Pos, pkg *Package, name string) *Label {
   336  	return &Label{object{pos: pos, pkg: pkg, name: name, typ: Typ[Invalid], color_: black}, false}
   337  }
   338  
   339  // A Builtin represents a built-in function.
   340  // Builtins don't have a valid type.
   341  type Builtin struct {
   342  	object
   343  	id builtinId
   344  }
   345  
   346  func newBuiltin(id builtinId) *Builtin {
   347  	return &Builtin{object{name: predeclaredFuncs[id].name, typ: Typ[Invalid], color_: black}, id}
   348  }
   349  
   350  // Nil represents the predeclared value nil.
   351  type Nil struct {
   352  	object
   353  }
   354  
   355  func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
   356  	var tname *TypeName
   357  	typ := obj.Type()
   358  
   359  	switch obj := obj.(type) {
   360  	case *PkgName:
   361  		fmt.Fprintf(buf, "package %s", obj.Name())
   362  		if path := obj.imported.path; path != "" && path != obj.name {
   363  			fmt.Fprintf(buf, " (%q)", path)
   364  		}
   365  		return
   366  
   367  	case *Const:
   368  		buf.WriteString("const")
   369  
   370  	case *TypeName:
   371  		tname = obj
   372  		buf.WriteString("type")
   373  
   374  	case *Var:
   375  		if obj.isField {
   376  			buf.WriteString("field")
   377  		} else {
   378  			buf.WriteString("var")
   379  		}
   380  
   381  	case *Func:
   382  		buf.WriteString("func ")
   383  		writeFuncName(buf, obj, qf)
   384  		if typ != nil {
   385  			WriteSignature(buf, typ.(*Signature), qf)
   386  		}
   387  		return
   388  
   389  	case *Label:
   390  		buf.WriteString("label")
   391  		typ = nil
   392  
   393  	case *Builtin:
   394  		buf.WriteString("builtin")
   395  		typ = nil
   396  
   397  	case *Nil:
   398  		buf.WriteString("nil")
   399  		return
   400  
   401  	default:
   402  		panic(fmt.Sprintf("writeObject(%T)", obj))
   403  	}
   404  
   405  	buf.WriteByte(' ')
   406  
   407  	// For package-level objects, qualify the name.
   408  	if obj.Pkg() != nil && obj.Pkg().scope.Lookup(obj.Name()) == obj {
   409  		writePackage(buf, obj.Pkg(), qf)
   410  	}
   411  	buf.WriteString(obj.Name())
   412  
   413  	if typ == nil {
   414  		return
   415  	}
   416  
   417  	if tname != nil {
   418  		// We have a type object: Don't print anything more for
   419  		// basic types since there's no more information (names
   420  		// are the same; see also comment in TypeName.IsAlias).
   421  		if _, ok := typ.(*Basic); ok {
   422  			return
   423  		}
   424  		if tname.IsAlias() {
   425  			buf.WriteString(" =")
   426  		} else {
   427  			typ = under(typ)
   428  		}
   429  	}
   430  
   431  	buf.WriteByte(' ')
   432  	WriteType(buf, typ, qf)
   433  }
   434  
   435  func writePackage(buf *bytes.Buffer, pkg *Package, qf Qualifier) {
   436  	if pkg == nil {
   437  		return
   438  	}
   439  	var s string
   440  	if qf != nil {
   441  		s = qf(pkg)
   442  	} else {
   443  		s = pkg.Path()
   444  	}
   445  	if s != "" {
   446  		buf.WriteString(s)
   447  		buf.WriteByte('.')
   448  	}
   449  }
   450  
   451  // ObjectString returns the string form of obj.
   452  // The Qualifier controls the printing of
   453  // package-level objects, and may be nil.
   454  func ObjectString(obj Object, qf Qualifier) string {
   455  	var buf bytes.Buffer
   456  	writeObject(&buf, obj, qf)
   457  	return buf.String()
   458  }
   459  
   460  func (obj *PkgName) String() string  { return ObjectString(obj, nil) }
   461  func (obj *Const) String() string    { return ObjectString(obj, nil) }
   462  func (obj *TypeName) String() string { return ObjectString(obj, nil) }
   463  func (obj *Var) String() string      { return ObjectString(obj, nil) }
   464  func (obj *Func) String() string     { return ObjectString(obj, nil) }
   465  func (obj *Label) String() string    { return ObjectString(obj, nil) }
   466  func (obj *Builtin) String() string  { return ObjectString(obj, nil) }
   467  func (obj *Nil) String() string      { return ObjectString(obj, nil) }
   468  
   469  func writeFuncName(buf *bytes.Buffer, f *Func, qf Qualifier) {
   470  	if f.typ != nil {
   471  		sig := f.typ.(*Signature)
   472  		if recv := sig.Recv(); recv != nil {
   473  			buf.WriteByte('(')
   474  			if _, ok := recv.Type().(*Interface); ok {
   475  				// gcimporter creates abstract methods of
   476  				// named interfaces using the interface type
   477  				// (not the named type) as the receiver.
   478  				// Don't print it in full.
   479  				buf.WriteString("interface")
   480  			} else {
   481  				WriteType(buf, recv.Type(), qf)
   482  			}
   483  			buf.WriteByte(')')
   484  			buf.WriteByte('.')
   485  		} else if f.pkg != nil {
   486  			writePackage(buf, f.pkg, qf)
   487  		}
   488  	}
   489  	buf.WriteString(f.name)
   490  }
   491  

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