object.go

Documentation: cmd/compile/internal/types2

     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 types2
     6  
     7  import (
     8  	"bytes"
     9  	"cmd/compile/internal/syntax"
    10  	"fmt"
    11  	"go/constant"
    12  	"strings"
    13  	"unicode"
    14  	"unicode/utf8"
    15  )
    16  
    17  // An Object describes a named language entity such as a package,
    18  // constant, type, variable, function (incl. methods), or label.
    19  // All objects implement the Object interface.
    20  type Object interface {
    21  	Parent() *Scope  // scope in which this object is declared; nil for methods and struct fields
    22  	Pos() syntax.Pos // position of object identifier in declaration
    23  	Pkg() *Package   // package to which this object belongs; nil for labels and objects in the Universe scope
    24  	Name() string    // package local object name
    25  	Type() Type      // object type
    26  	Exported() bool  // reports whether the name starts with a capital letter
    27  	Id() string      // object name if exported, qualified name if not exported (see func Id)
    28  
    29  	// String returns a human-readable string of the object.
    30  	String() string
    31  
    32  	// order reflects a package-level object's source order: if object
    33  	// a is before object b in the source, then a.order() < b.order().
    34  	// order returns a value > 0 for package-level objects; it returns
    35  	// 0 for all other objects (including objects in file scopes).
    36  	order() uint32
    37  
    38  	// color returns the object's color.
    39  	color() color
    40  
    41  	// setType sets the type of the object.
    42  	setType(Type)
    43  
    44  	// setOrder sets the order number of the object. It must be > 0.
    45  	setOrder(uint32)
    46  
    47  	// setColor sets the object's color. It must not be white.
    48  	setColor(color color)
    49  
    50  	// setParent sets the parent scope of the object.
    51  	setParent(*Scope)
    52  
    53  	// sameId reports whether obj.Id() and Id(pkg, name) are the same.
    54  	// If foldCase is true, names are considered equal if they are equal with case folding
    55  	// and their packages are ignored (e.g., pkg1.m, pkg1.M, pkg2.m, and pkg2.M are all equal).
    56  	sameId(pkg *Package, name string, foldCase bool) bool
    57  
    58  	// scopePos returns the start position of the scope of this Object
    59  	scopePos() syntax.Pos
    60  
    61  	// setScopePos sets the start position of the scope for this Object.
    62  	setScopePos(pos syntax.Pos)
    63  }
    64  
    65  func isExported(name string) bool {
    66  	ch, _ := utf8.DecodeRuneInString(name)
    67  	return unicode.IsUpper(ch)
    68  }
    69  
    70  // Id returns name if it is exported, otherwise it
    71  // returns the name qualified with the package path.
    72  func Id(pkg *Package, name string) string {
    73  	if isExported(name) {
    74  		return name
    75  	}
    76  	// unexported names need the package path for differentiation
    77  	// (if there's no package, make sure we don't start with '.'
    78  	// as that may change the order of methods between a setup
    79  	// inside a package and outside a package - which breaks some
    80  	// tests)
    81  	path := "_"
    82  	// pkg is nil for objects in Universe scope and possibly types
    83  	// introduced via Eval (see also comment in object.sameId)
    84  	if pkg != nil && pkg.path != "" {
    85  		path = pkg.path
    86  	}
    87  	return path + "." + name
    88  }
    89  
    90  // An object implements the common parts of an Object.
    91  type object struct {
    92  	parent    *Scope
    93  	pos       syntax.Pos
    94  	pkg       *Package
    95  	name      string
    96  	typ       Type
    97  	order_    uint32
    98  	color_    color
    99  	scopePos_ syntax.Pos
   100  }
   101  
   102  // color encodes the color of an object (see Checker.objDecl for details).
   103  type color uint32
   104  
   105  // An object may be painted in one of three colors.
   106  // Color values other than white or black are considered grey.
   107  const (
   108  	white color = iota
   109  	black
   110  	grey // must be > white and black
   111  )
   112  
   113  func (c color) String() string {
   114  	switch c {
   115  	case white:
   116  		return "white"
   117  	case black:
   118  		return "black"
   119  	default:
   120  		return "grey"
   121  	}
   122  }
   123  
   124  // colorFor returns the (initial) color for an object depending on
   125  // whether its type t is known or not.
   126  func colorFor(t Type) color {
   127  	if t != nil {
   128  		return black
   129  	}
   130  	return white
   131  }
   132  
   133  // Parent returns the scope in which the object is declared.
   134  // The result is nil for methods and struct fields.
   135  func (obj *object) Parent() *Scope { return obj.parent }
   136  
   137  // Pos returns the declaration position of the object's identifier.
   138  func (obj *object) Pos() syntax.Pos { return obj.pos }
   139  
   140  // Pkg returns the package to which the object belongs.
   141  // The result is nil for labels and objects in the Universe scope.
   142  func (obj *object) Pkg() *Package { return obj.pkg }
   143  
   144  // Name returns the object's (package-local, unqualified) name.
   145  func (obj *object) Name() string { return obj.name }
   146  
   147  // Type returns the object's type.
   148  func (obj *object) Type() Type { return obj.typ }
   149  
   150  // Exported reports whether the object is exported (starts with a capital letter).
   151  // It doesn't take into account whether the object is in a local (function) scope
   152  // or not.
   153  func (obj *object) Exported() bool { return isExported(obj.name) }
   154  
   155  // Id is a wrapper for Id(obj.Pkg(), obj.Name()).
   156  func (obj *object) Id() string { return Id(obj.pkg, obj.name) }
   157  
   158  func (obj *object) String() string       { panic("abstract") }
   159  func (obj *object) order() uint32        { return obj.order_ }
   160  func (obj *object) color() color         { return obj.color_ }
   161  func (obj *object) scopePos() syntax.Pos { return obj.scopePos_ }
   162  
   163  func (obj *object) setParent(parent *Scope)    { obj.parent = parent }
   164  func (obj *object) setType(typ Type)           { obj.typ = typ }
   165  func (obj *object) setOrder(order uint32)      { assert(order > 0); obj.order_ = order }
   166  func (obj *object) setColor(color color)       { assert(color != white); obj.color_ = color }
   167  func (obj *object) setScopePos(pos syntax.Pos) { obj.scopePos_ = pos }
   168  
   169  func (obj *object) sameId(pkg *Package, name string, foldCase bool) bool {
   170  	// If we don't care about capitalization, we also ignore packages.
   171  	if foldCase && strings.EqualFold(obj.name, name) {
   172  		return true
   173  	}
   174  	// spec:
   175  	// "Two identifiers are different if they are spelled differently,
   176  	// or if they appear in different packages and are not exported.
   177  	// Otherwise, they are the same."
   178  	if obj.name != name {
   179  		return false
   180  	}
   181  	// obj.Name == name
   182  	if obj.Exported() {
   183  		return true
   184  	}
   185  	// not exported, so packages must be the same
   186  	return samePkg(obj.pkg, pkg)
   187  }
   188  
   189  // less reports whether object a is ordered before object b.
   190  //
   191  // Objects are ordered nil before non-nil, exported before
   192  // non-exported, then by name, and finally (for non-exported
   193  // functions) by package path.
   194  func (a *object) less(b *object) bool {
   195  	if a == b {
   196  		return false
   197  	}
   198  
   199  	// Nil before non-nil.
   200  	if a == nil {
   201  		return true
   202  	}
   203  	if b == nil {
   204  		return false
   205  	}
   206  
   207  	// Exported functions before non-exported.
   208  	ea := isExported(a.name)
   209  	eb := isExported(b.name)
   210  	if ea != eb {
   211  		return ea
   212  	}
   213  
   214  	// Order by name and then (for non-exported names) by package.
   215  	if a.name != b.name {
   216  		return a.name < b.name
   217  	}
   218  	if !ea {
   219  		return a.pkg.path < b.pkg.path
   220  	}
   221  
   222  	return false
   223  }
   224  
   225  // A PkgName represents an imported Go package.
   226  // PkgNames don't have a type.
   227  type PkgName struct {
   228  	object
   229  	imported *Package
   230  	used     bool // set if the package was used
   231  }
   232  
   233  // NewPkgName returns a new PkgName object representing an imported package.
   234  // The remaining arguments set the attributes found with all Objects.
   235  func NewPkgName(pos syntax.Pos, pkg *Package, name string, imported *Package) *PkgName {
   236  	return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, nopos}, imported, false}
   237  }
   238  
   239  // Imported returns the package that was imported.
   240  // It is distinct from Pkg(), which is the package containing the import statement.
   241  func (obj *PkgName) Imported() *Package { return obj.imported }
   242  
   243  // A Const represents a declared constant.
   244  type Const struct {
   245  	object
   246  	val constant.Value
   247  }
   248  
   249  // NewConst returns a new constant with value val.
   250  // The remaining arguments set the attributes found with all Objects.
   251  func NewConst(pos syntax.Pos, pkg *Package, name string, typ Type, val constant.Value) *Const {
   252  	return &Const{object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, val}
   253  }
   254  
   255  // Val returns the constant's value.
   256  func (obj *Const) Val() constant.Value { return obj.val }
   257  
   258  func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
   259  
   260  // A TypeName represents a name for a (defined or alias) type.
   261  type TypeName struct {
   262  	object
   263  }
   264  
   265  // NewTypeName returns a new type name denoting the given typ.
   266  // The remaining arguments set the attributes found with all Objects.
   267  //
   268  // The typ argument may be a defined (Named) type or an alias type.
   269  // It may also be nil such that the returned TypeName can be used as
   270  // argument for NewNamed, which will set the TypeName's type as a side-
   271  // effect.
   272  func NewTypeName(pos syntax.Pos, pkg *Package, name string, typ Type) *TypeName {
   273  	return &TypeName{object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}}
   274  }
   275  
   276  // NewTypeNameLazy returns a new defined type like NewTypeName, but it
   277  // lazily calls resolve to finish constructing the Named object.
   278  func NewTypeNameLazy(pos syntax.Pos, pkg *Package, name string, load func(named *Named) (tparams []*TypeParam, underlying Type, methods []*Func)) *TypeName {
   279  	obj := NewTypeName(pos, pkg, name, nil)
   280  	NewNamed(obj, nil, nil).loader = load
   281  	return obj
   282  }
   283  
   284  // IsAlias reports whether obj is an alias name for a type.
   285  func (obj *TypeName) IsAlias() bool {
   286  	switch t := obj.typ.(type) {
   287  	case nil:
   288  		return false
   289  	// case *Alias:
   290  	//	handled by default case
   291  	case *Basic:
   292  		// unsafe.Pointer is not an alias.
   293  		if obj.pkg == Unsafe {
   294  			return false
   295  		}
   296  		// Any user-defined type name for a basic type is an alias for a
   297  		// basic type (because basic types are pre-declared in the Universe
   298  		// scope, outside any package scope), and so is any type name with
   299  		// a different name than the name of the basic type it refers to.
   300  		// Additionally, we need to look for "byte" and "rune" because they
   301  		// are aliases but have the same names (for better error messages).
   302  		return obj.pkg != nil || t.name != obj.name || t == universeByte || t == universeRune
   303  	case *Named:
   304  		return obj != t.obj
   305  	case *TypeParam:
   306  		return obj != t.obj
   307  	default:
   308  		return true
   309  	}
   310  }
   311  
   312  // A Variable represents a declared variable (including function parameters and results, and struct fields).
   313  type Var struct {
   314  	object
   315  	embedded bool // if set, the variable is an embedded struct field, and name is the type name
   316  	isField  bool // var is struct field
   317  	used     bool // set if the variable was used
   318  	origin   *Var // if non-nil, the Var from which this one was instantiated
   319  }
   320  
   321  // NewVar returns a new variable.
   322  // The arguments set the attributes found with all Objects.
   323  func NewVar(pos syntax.Pos, pkg *Package, name string, typ Type) *Var {
   324  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}}
   325  }
   326  
   327  // NewParam returns a new variable representing a function parameter.
   328  func NewParam(pos syntax.Pos, pkg *Package, name string, typ Type) *Var {
   329  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, used: true} // parameters are always 'used'
   330  }
   331  
   332  // NewField returns a new variable representing a struct field.
   333  // For embedded fields, the name is the unqualified type name
   334  // under which the field is accessible.
   335  func NewField(pos syntax.Pos, pkg *Package, name string, typ Type, embedded bool) *Var {
   336  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, embedded: embedded, isField: true}
   337  }
   338  
   339  // Anonymous reports whether the variable is an embedded field.
   340  // Same as Embedded; only present for backward-compatibility.
   341  func (obj *Var) Anonymous() bool { return obj.embedded }
   342  
   343  // Embedded reports whether the variable is an embedded field.
   344  func (obj *Var) Embedded() bool { return obj.embedded }
   345  
   346  // IsField reports whether the variable is a struct field.
   347  func (obj *Var) IsField() bool { return obj.isField }
   348  
   349  // Origin returns the canonical Var for its receiver, i.e. the Var object
   350  // recorded in Info.Defs.
   351  //
   352  // For synthetic Vars created during instantiation (such as struct fields or
   353  // function parameters that depend on type arguments), this will be the
   354  // corresponding Var on the generic (uninstantiated) type. For all other Vars
   355  // Origin returns the receiver.
   356  func (obj *Var) Origin() *Var {
   357  	if obj.origin != nil {
   358  		return obj.origin
   359  	}
   360  	return obj
   361  }
   362  
   363  func (*Var) isDependency() {} // a variable may be a dependency of an initialization expression
   364  
   365  // A Func represents a declared function, concrete method, or abstract
   366  // (interface) method. Its Type() is always a *Signature.
   367  // An abstract method may belong to many interfaces due to embedding.
   368  type Func struct {
   369  	object
   370  	hasPtrRecv_ bool  // only valid for methods that don't have a type yet; use hasPtrRecv() to read
   371  	origin      *Func // if non-nil, the Func from which this one was instantiated
   372  }
   373  
   374  // NewFunc returns a new function with the given signature, representing
   375  // the function's type.
   376  func NewFunc(pos syntax.Pos, pkg *Package, name string, sig *Signature) *Func {
   377  	var typ Type
   378  	if sig != nil {
   379  		typ = sig
   380  	} else {
   381  		// Don't store a (typed) nil *Signature.
   382  		// We can't simply replace it with new(Signature) either,
   383  		// as this would violate object.{Type,color} invariants.
   384  		// TODO(adonovan): propose to disallow NewFunc with nil *Signature.
   385  	}
   386  	return &Func{object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, false, nil}
   387  }
   388  
   389  // Signature returns the signature (type) of the function or method.
   390  func (obj *Func) Signature() *Signature {
   391  	if obj.typ != nil {
   392  		return obj.typ.(*Signature) // normal case
   393  	}
   394  	// No signature: Signature was called either:
   395  	// - within go/types, before a FuncDecl's initially
   396  	//   nil Func.Type was lazily populated, indicating
   397  	//   a types bug; or
   398  	// - by a client after NewFunc(..., nil),
   399  	//   which is arguably a client bug, but we need a
   400  	//   proposal to tighten NewFunc's precondition.
   401  	// For now, return a trivial signature.
   402  	return new(Signature)
   403  }
   404  
   405  // FullName returns the package- or receiver-type-qualified name of
   406  // function or method obj.
   407  func (obj *Func) FullName() string {
   408  	var buf bytes.Buffer
   409  	writeFuncName(&buf, obj, nil)
   410  	return buf.String()
   411  }
   412  
   413  // Scope returns the scope of the function's body block.
   414  // The result is nil for imported or instantiated functions and methods
   415  // (but there is also no mechanism to get to an instantiated function).
   416  func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
   417  
   418  // Origin returns the canonical Func for its receiver, i.e. the Func object
   419  // recorded in Info.Defs.
   420  //
   421  // For synthetic functions created during instantiation (such as methods on an
   422  // instantiated Named type or interface methods that depend on type arguments),
   423  // this will be the corresponding Func on the generic (uninstantiated) type.
   424  // For all other Funcs Origin returns the receiver.
   425  func (obj *Func) Origin() *Func {
   426  	if obj.origin != nil {
   427  		return obj.origin
   428  	}
   429  	return obj
   430  }
   431  
   432  // Pkg returns the package to which the function belongs.
   433  //
   434  // The result is nil for methods of types in the Universe scope,
   435  // like method Error of the error built-in interface type.
   436  func (obj *Func) Pkg() *Package { return obj.object.Pkg() }
   437  
   438  // hasPtrRecv reports whether the receiver is of the form *T for the given method obj.
   439  func (obj *Func) hasPtrRecv() bool {
   440  	// If a method's receiver type is set, use that as the source of truth for the receiver.
   441  	// Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
   442  	// signature. We may reach here before the signature is fully set up: we must explicitly
   443  	// check if the receiver is set (we cannot just look for non-nil obj.typ).
   444  	if sig, _ := obj.typ.(*Signature); sig != nil && sig.recv != nil {
   445  		_, isPtr := deref(sig.recv.typ)
   446  		return isPtr
   447  	}
   448  
   449  	// If a method's type is not set it may be a method/function that is:
   450  	// 1) client-supplied (via NewFunc with no signature), or
   451  	// 2) internally created but not yet type-checked.
   452  	// For case 1) we can't do anything; the client must know what they are doing.
   453  	// For case 2) we can use the information gathered by the resolver.
   454  	return obj.hasPtrRecv_
   455  }
   456  
   457  func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
   458  
   459  // A Label represents a declared label.
   460  // Labels don't have a type.
   461  type Label struct {
   462  	object
   463  	used bool // set if the label was used
   464  }
   465  
   466  // NewLabel returns a new label.
   467  func NewLabel(pos syntax.Pos, pkg *Package, name string) *Label {
   468  	return &Label{object{pos: pos, pkg: pkg, name: name, typ: Typ[Invalid], color_: black}, false}
   469  }
   470  
   471  // A Builtin represents a built-in function.
   472  // Builtins don't have a valid type.
   473  type Builtin struct {
   474  	object
   475  	id builtinId
   476  }
   477  
   478  func newBuiltin(id builtinId) *Builtin {
   479  	return &Builtin{object{name: predeclaredFuncs[id].name, typ: Typ[Invalid], color_: black}, id}
   480  }
   481  
   482  // Nil represents the predeclared value nil.
   483  type Nil struct {
   484  	object
   485  }
   486  
   487  func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
   488  	var tname *TypeName
   489  	typ := obj.Type()
   490  
   491  	switch obj := obj.(type) {
   492  	case *PkgName:
   493  		fmt.Fprintf(buf, "package %s", obj.Name())
   494  		if path := obj.imported.path; path != "" && path != obj.name {
   495  			fmt.Fprintf(buf, " (%q)", path)
   496  		}
   497  		return
   498  
   499  	case *Const:
   500  		buf.WriteString("const")
   501  
   502  	case *TypeName:
   503  		tname = obj
   504  		buf.WriteString("type")
   505  		if isTypeParam(typ) {
   506  			buf.WriteString(" parameter")
   507  		}
   508  
   509  	case *Var:
   510  		if obj.isField {
   511  			buf.WriteString("field")
   512  		} else {
   513  			buf.WriteString("var")
   514  		}
   515  
   516  	case *Func:
   517  		buf.WriteString("func ")
   518  		writeFuncName(buf, obj, qf)
   519  		if typ != nil {
   520  			WriteSignature(buf, typ.(*Signature), qf)
   521  		}
   522  		return
   523  
   524  	case *Label:
   525  		buf.WriteString("label")
   526  		typ = nil
   527  
   528  	case *Builtin:
   529  		buf.WriteString("builtin")
   530  		typ = nil
   531  
   532  	case *Nil:
   533  		buf.WriteString("nil")
   534  		return
   535  
   536  	default:
   537  		panic(fmt.Sprintf("writeObject(%T)", obj))
   538  	}
   539  
   540  	buf.WriteByte(' ')
   541  
   542  	// For package-level objects, qualify the name.
   543  	if obj.Pkg() != nil && obj.Pkg().scope.Lookup(obj.Name()) == obj {
   544  		buf.WriteString(packagePrefix(obj.Pkg(), qf))
   545  	}
   546  	buf.WriteString(obj.Name())
   547  
   548  	if typ == nil {
   549  		return
   550  	}
   551  
   552  	if tname != nil {
   553  		switch t := typ.(type) {
   554  		case *Basic:
   555  			// Don't print anything more for basic types since there's
   556  			// no more information.
   557  			return
   558  		case *Named:
   559  			if t.TypeParams().Len() > 0 {
   560  				newTypeWriter(buf, qf).tParamList(t.TypeParams().list())
   561  			}
   562  		}
   563  		if tname.IsAlias() {
   564  			buf.WriteString(" =")
   565  			if alias, ok := typ.(*Alias); ok { // materialized? (gotypesalias=1)
   566  				typ = alias.fromRHS
   567  			}
   568  		} else if t, _ := typ.(*TypeParam); t != nil {
   569  			typ = t.bound
   570  		} else {
   571  			// TODO(gri) should this be fromRHS for *Named?
   572  			// (See discussion in #66559.)
   573  			typ = under(typ)
   574  		}
   575  	}
   576  
   577  	// Special handling for any: because WriteType will format 'any' as 'any',
   578  	// resulting in the object string `type any = any` rather than `type any =
   579  	// interface{}`. To avoid this, swap in a different empty interface.
   580  	if obj.Name() == "any" && obj.Parent() == Universe {
   581  		assert(Identical(typ, &emptyInterface))
   582  		typ = &emptyInterface
   583  	}
   584  
   585  	buf.WriteByte(' ')
   586  	WriteType(buf, typ, qf)
   587  }
   588  
   589  func packagePrefix(pkg *Package, qf Qualifier) string {
   590  	if pkg == nil {
   591  		return ""
   592  	}
   593  	var s string
   594  	if qf != nil {
   595  		s = qf(pkg)
   596  	} else {
   597  		s = pkg.Path()
   598  	}
   599  	if s != "" {
   600  		s += "."
   601  	}
   602  	return s
   603  }
   604  
   605  // ObjectString returns the string form of obj.
   606  // The Qualifier controls the printing of
   607  // package-level objects, and may be nil.
   608  func ObjectString(obj Object, qf Qualifier) string {
   609  	var buf bytes.Buffer
   610  	writeObject(&buf, obj, qf)
   611  	return buf.String()
   612  }
   613  
   614  func (obj *PkgName) String() string  { return ObjectString(obj, nil) }
   615  func (obj *Const) String() string    { return ObjectString(obj, nil) }
   616  func (obj *TypeName) String() string { return ObjectString(obj, nil) }
   617  func (obj *Var) String() string      { return ObjectString(obj, nil) }
   618  func (obj *Func) String() string     { return ObjectString(obj, nil) }
   619  func (obj *Label) String() string    { return ObjectString(obj, nil) }
   620  func (obj *Builtin) String() string  { return ObjectString(obj, nil) }
   621  func (obj *Nil) String() string      { return ObjectString(obj, nil) }
   622  
   623  func writeFuncName(buf *bytes.Buffer, f *Func, qf Qualifier) {
   624  	if f.typ != nil {
   625  		sig := f.typ.(*Signature)
   626  		if recv := sig.Recv(); recv != nil {
   627  			buf.WriteByte('(')
   628  			if _, ok := recv.Type().(*Interface); ok {
   629  				// gcimporter creates abstract methods of
   630  				// named interfaces using the interface type
   631  				// (not the named type) as the receiver.
   632  				// Don't print it in full.
   633  				buf.WriteString("interface")
   634  			} else {
   635  				WriteType(buf, recv.Type(), qf)
   636  			}
   637  			buf.WriteByte(')')
   638  			buf.WriteByte('.')
   639  		} else if f.pkg != nil {
   640  			buf.WriteString(packagePrefix(f.pkg, qf))
   641  		}
   642  	}
   643  	buf.WriteString(f.name)
   644  }
   645
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