alias.go

     1  // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
     2  // Source: ../../cmd/compile/internal/types2/alias.go
     3  
     4  // Copyright 2023 The Go Authors. All rights reserved.
     5  // Use of this source code is governed by a BSD-style
     6  // license that can be found in the LICENSE file.
     7  
     8  package types
     9  
    10  import (
    11  	"go/token"
    12  )
    13  
    14  // An Alias represents an alias type.
    15  //
    16  // Alias types are created by alias declarations such as:
    17  //
    18  //	type A = int
    19  //
    20  // The type on the right-hand side of the declaration can be accessed
    21  // using [Alias.Rhs]. This type may itself be an alias.
    22  // Call [Unalias] to obtain the first non-alias type in a chain of
    23  // alias type declarations.
    24  //
    25  // Like a defined ([Named]) type, an alias type has a name.
    26  // Use the [Alias.Obj] method to access its [TypeName] object.
    27  //
    28  // Historically, Alias types were not materialized so that, in the example
    29  // above, A's type was represented by a Basic (int), not an Alias
    30  // whose [Alias.Rhs] is int. But Go 1.24 allows you to declare an
    31  // alias type with type parameters or arguments:
    32  //
    33  //	type Set[K comparable] = map[K]bool
    34  //	s := make(Set[String])
    35  //
    36  // and this requires that Alias types be materialized. Use the
    37  // [Alias.TypeParams] and [Alias.TypeArgs] methods to access them.
    38  //
    39  // To ease the transition, the Alias type was introduced in go1.22,
    40  // but the type-checker would not construct values of this type unless
    41  // the GODEBUG=gotypesalias=1 environment variable was provided.
    42  // Starting in go1.23, this variable is enabled by default.
    43  // This setting also causes the predeclared type "any" to be
    44  // represented as an Alias, not a bare [Interface].
    45  type Alias struct {
    46  	obj     *TypeName      // corresponding declared alias object
    47  	orig    *Alias         // original, uninstantiated alias
    48  	tparams *TypeParamList // type parameters, or nil
    49  	targs   *TypeList      // type arguments, or nil
    50  	fromRHS Type           // RHS of type alias declaration; may be an alias
    51  	actual  Type           // actual (aliased) type; never an alias
    52  }
    53  
    54  // NewAlias creates a new Alias type with the given type name and rhs.
    55  // If rhs is nil, the alias is incomplete.
    56  func NewAlias(obj *TypeName, rhs Type) *Alias {
    57  	alias := (*Checker)(nil).newAlias(obj, rhs)
    58  	// Ensure that alias.actual is set (#65455).
    59  	alias.cleanup()
    60  	return alias
    61  }
    62  
    63  // Obj returns the type name for the declaration defining the alias type a.
    64  // For instantiated types, this is same as the type name of the origin type.
    65  func (a *Alias) Obj() *TypeName { return a.orig.obj }
    66  
    67  func (a *Alias) String() string { return TypeString(a, nil) }
    68  
    69  // Underlying returns the [underlying type] of the alias type a, which is the
    70  // underlying type of the aliased type. Underlying types are never Named,
    71  // TypeParam, or Alias types.
    72  //
    73  // [underlying type]: https://go.dev/ref/spec#Underlying_types.
    74  func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
    75  
    76  // Origin returns the generic Alias type of which a is an instance.
    77  // If a is not an instance of a generic alias, Origin returns a.
    78  func (a *Alias) Origin() *Alias { return a.orig }
    79  
    80  // TypeParams returns the type parameters of the alias type a, or nil.
    81  // A generic Alias and its instances have the same type parameters.
    82  func (a *Alias) TypeParams() *TypeParamList { return a.tparams }
    83  
    84  // SetTypeParams sets the type parameters of the alias type a.
    85  // The alias a must not have type arguments.
    86  func (a *Alias) SetTypeParams(tparams []*TypeParam) {
    87  	assert(a.targs == nil)
    88  	a.tparams = bindTParams(tparams)
    89  }
    90  
    91  // TypeArgs returns the type arguments used to instantiate the Alias type.
    92  // If a is not an instance of a generic alias, the result is nil.
    93  func (a *Alias) TypeArgs() *TypeList { return a.targs }
    94  
    95  // Rhs returns the type R on the right-hand side of an alias
    96  // declaration "type A = R", which may be another alias.
    97  func (a *Alias) Rhs() Type { return a.fromRHS }
    98  
    99  // Unalias returns t if it is not an alias type;
   100  // otherwise it follows t's alias chain until it
   101  // reaches a non-alias type which is then returned.
   102  // Consequently, the result is never an alias type.
   103  // Returns nil if the alias is incomplete.
   104  func Unalias(t Type) Type {
   105  	if a0, _ := t.(*Alias); a0 != nil {
   106  		return unalias(a0)
   107  	}
   108  	return t
   109  }
   110  
   111  func unalias(a0 *Alias) Type {
   112  	if a0.actual != nil {
   113  		return a0.actual
   114  	}
   115  	var t Type
   116  	for a := a0; a != nil; a, _ = t.(*Alias) {
   117  		t = a.fromRHS
   118  	}
   119  	// It's fine to memoize nil types since it's the zero value for actual.
   120  	// It accomplishes nothing.
   121  	a0.actual = t
   122  	return t
   123  }
   124  
   125  // asNamed returns t as *Named if that is t's
   126  // actual type. It returns nil otherwise.
   127  func asNamed(t Type) *Named {
   128  	n, _ := Unalias(t).(*Named)
   129  	return n
   130  }
   131  
   132  // newAlias creates a new Alias type with the given type name and rhs.
   133  // If rhs is nil, the alias is incomplete.
   134  func (check *Checker) newAlias(obj *TypeName, rhs Type) *Alias {
   135  	a := new(Alias)
   136  	a.obj = obj
   137  	a.orig = a
   138  	a.fromRHS = rhs
   139  	if obj.typ == nil {
   140  		obj.typ = a
   141  	}
   142  
   143  	// Ensure that a.actual is set at the end of type checking.
   144  	if check != nil {
   145  		check.needsCleanup(a)
   146  	}
   147  
   148  	return a
   149  }
   150  
   151  // newAliasInstance creates a new alias instance for the given origin and type
   152  // arguments, recording pos as the position of its synthetic object (for error
   153  // reporting).
   154  func (check *Checker) newAliasInstance(pos token.Pos, orig *Alias, targs []Type, expanding *Named, ctxt *Context) *Alias {
   155  	assert(len(targs) > 0)
   156  	obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil)
   157  	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), expanding, ctxt)
   158  	res := check.newAlias(obj, rhs)
   159  	res.orig = orig
   160  	res.tparams = orig.tparams
   161  	res.targs = newTypeList(targs)
   162  	return res
   163  }
   164  
   165  func (a *Alias) cleanup() {
   166  	// Ensure a.actual is set before types are published,
   167  	// so unalias is a pure "getter", not a "setter".
   168  	unalias(a)
   169  }
   170
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