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  type Alias struct {
    28  	obj     *TypeName      // corresponding declared alias object
    29  	orig    *Alias         // original, uninstantiated alias
    30  	tparams *TypeParamList // type parameters, or nil
    31  	targs   *TypeList      // type arguments, or nil
    32  	fromRHS Type           // RHS of type alias declaration; may be an alias
    33  	actual  Type           // actual (aliased) type; never an alias
    34  }
    35  
    36  // NewAlias creates a new Alias type with the given type name and rhs.
    37  // If rhs is nil, the alias is incomplete.
    38  func NewAlias(obj *TypeName, rhs Type) *Alias {
    39  	alias := (*Checker)(nil).newAlias(obj, rhs)
    40  	// Ensure that alias.actual is set (#65455).
    41  	alias.cleanup()
    42  	return alias
    43  }
    44  
    45  // Obj returns the type name for the declaration defining the alias type a.
    46  // For instantiated types, this is same as the type name of the origin type.
    47  func (a *Alias) Obj() *TypeName { return a.orig.obj }
    48  
    49  func (a *Alias) String() string { return TypeString(a, nil) }
    50  
    51  // Underlying returns the [underlying type] of the alias type a, which is the
    52  // underlying type of the aliased type. Underlying types are never Named,
    53  // TypeParam, or Alias types.
    54  //
    55  // [underlying type]: https://go.dev/ref/spec#Underlying_types.
    56  func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
    57  
    58  // Origin returns the generic Alias type of which a is an instance.
    59  // If a is not an instance of a generic alias, Origin returns a.
    60  func (a *Alias) Origin() *Alias { return a.orig }
    61  
    62  // TypeParams returns the type parameters of the alias type a, or nil.
    63  // A generic Alias and its instances have the same type parameters.
    64  func (a *Alias) TypeParams() *TypeParamList { return a.tparams }
    65  
    66  // SetTypeParams sets the type parameters of the alias type a.
    67  // The alias a must not have type arguments.
    68  func (a *Alias) SetTypeParams(tparams []*TypeParam) {
    69  	assert(a.targs == nil)
    70  	a.tparams = bindTParams(tparams)
    71  }
    72  
    73  // TypeArgs returns the type arguments used to instantiate the Alias type.
    74  // If a is not an instance of a generic alias, the result is nil.
    75  func (a *Alias) TypeArgs() *TypeList { return a.targs }
    76  
    77  // Rhs returns the type R on the right-hand side of an alias
    78  // declaration "type A = R", which may be another alias.
    79  func (a *Alias) Rhs() Type { return a.fromRHS }
    80  
    81  // Unalias returns t if it is not an alias type;
    82  // otherwise it follows t's alias chain until it
    83  // reaches a non-alias type which is then returned.
    84  // Consequently, the result is never an alias type.
    85  // Returns nil if the alias is incomplete.
    86  func Unalias(t Type) Type {
    87  	if a0, _ := t.(*Alias); a0 != nil {
    88  		return unalias(a0)
    89  	}
    90  	return t
    91  }
    92  
    93  func unalias(a0 *Alias) Type {
    94  	if a0.actual != nil {
    95  		return a0.actual
    96  	}
    97  	var t Type
    98  	for a := a0; a != nil; a, _ = t.(*Alias) {
    99  		t = a.fromRHS
   100  	}
   101  	// It's fine to memoize nil types since it's the zero value for actual.
   102  	// It accomplishes nothing.
   103  	a0.actual = t
   104  	return t
   105  }
   106  
   107  // asNamed returns t as *Named if that is t's
   108  // actual type. It returns nil otherwise.
   109  func asNamed(t Type) *Named {
   110  	n, _ := Unalias(t).(*Named)
   111  	return n
   112  }
   113  
   114  // newAlias creates a new Alias type with the given type name and rhs.
   115  // If rhs is nil, the alias is incomplete.
   116  func (check *Checker) newAlias(obj *TypeName, rhs Type) *Alias {
   117  	a := new(Alias)
   118  	a.obj = obj
   119  	a.orig = a
   120  	a.fromRHS = rhs
   121  	if obj.typ == nil {
   122  		obj.typ = a
   123  	}
   124  
   125  	// Ensure that a.actual is set at the end of type checking.
   126  	if check != nil {
   127  		check.needsCleanup(a)
   128  	}
   129  
   130  	return a
   131  }
   132  
   133  // newAliasInstance creates a new alias instance for the given origin and type
   134  // arguments, recording pos as the position of its synthetic object (for error
   135  // reporting).
   136  func (check *Checker) newAliasInstance(pos token.Pos, orig *Alias, targs []Type, expanding *Named, ctxt *Context) *Alias {
   137  	assert(len(targs) > 0)
   138  	obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil)
   139  	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), expanding, ctxt)
   140  	res := check.newAlias(obj, rhs)
   141  	res.orig = orig
   142  	res.tparams = orig.tparams
   143  	res.targs = newTypeList(targs)
   144  	return res
   145  }
   146  
   147  func (a *Alias) cleanup() {
   148  	// Ensure a.actual is set before types are published,
   149  	// so unalias is a pure "getter", not a "setter".
   150  	unalias(a)
   151  }
   152
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