)
// An Alias represents an alias type.
-// Whether or not Alias types are created is controlled by the
-// gotypesalias setting with the GODEBUG environment variable.
-// For gotypesalias=1, alias declarations produce an Alias type.
-// Otherwise, the alias information is only in the type name,
-// which points directly to the actual (aliased) type.
+//
+// Alias types are created by alias declarations such as:
+//
+// type A = int
+//
+// The type on the right-hand side of the declaration can be accessed
+// using [Alias.Rhs]. This type may itself be an alias.
+// Call [Unalias] to obtain the first non-alias type in a chain of
+// alias type declarations.
+//
+// Like a defined ([Named]) type, an alias type has a name.
+// Use the [Alias.Obj] method to access its [TypeName] object.
+//
+// Historically, Alias types were not materialized so that, in the example
+// above, A's type was represented by a Basic (int), not an Alias
+// whose [Alias.Rhs] is int. But Go 1.24 allows you to declare an
+// alias type with type parameters or arguments:
+//
+// type Set[K comparable] = map[K]bool
+// s := make(Set[String])
+//
+// and this requires that Alias types be materialized. Use the
+// [Alias.TypeParams] and [Alias.TypeArgs] methods to access them.
+//
+// To ease the transition, the Alias type was introduced in go1.22,
+// but the type-checker would not construct values of this type unless
+// the GODEBUG=gotypesalias=1 environment variable was provided.
+// Starting in go1.23, this variable is enabled by default.
+// This setting also causes the predeclared type "any" to be
+// represented as an Alias, not a bare [Interface].
type Alias struct {
obj *TypeName // corresponding declared alias object
orig *Alias // original, uninstantiated alias
// in its "lineage".
// A Named represents a named (defined) type.
+//
+// A declaration such as:
+//
+// type S struct { ... }
+//
+// creates a defined type whose underlying type is a struct,
+// and binds this type to the object S, a [TypeName].
+// Use [Named.Underlying] to access the underlying type.
+// Use [Named.Obj] to obtain the object S.
+//
+// Before type aliases (Go 1.9), the spec called defined types "named types".
type Named struct {
check *Checker // non-nil during type-checking; nil otherwise
obj *TypeName // corresponding declared object for declared types; see above for instantiated types
"unicode/utf8"
)
-// An Object describes a named language entity such as a package,
-// constant, type, variable, function (incl. methods), or label.
-// All objects implement the Object interface.
+// An Object is a named language entity.
+// An Object may be a constant ([Const]), type name ([TypeName]),
+// variable or struct field ([Var]), function or method ([Func]),
+// imported package ([PkgName]), label ([Label]),
+// built-in function ([Builtin]),
+// or the predeclared identifier 'nil' ([Nil]).
+//
+// The environment, which is structured as a tree of Scopes,
+// maps each name to the unique Object that it denotes.
type Object interface {
Parent() *Scope // scope in which this object is declared; nil for methods and struct fields
Pos() syntax.Pos // position of object identifier in declaration
Id() string // object name if exported, qualified name if not exported (see func Id)
// String returns a human-readable string of the object.
+ // Use [ObjectString] to control how package names are formatted in the string.
String() string
// order reflects a package-level object's source order: if object
func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
-// A TypeName represents a name for a (defined or alias) type.
+// A TypeName is an [Object] that represents a type with a name:
+// a defined type ([Named]),
+// an alias type ([Alias]),
+// a type parameter ([TypeParam]),
+// or a predeclared type such as int or error.
type TypeName struct {
object
}
// each call, starting with 1. It may be called concurrently.
func nextID() uint64 { return uint64(lastID.Add(1)) }
-// A TypeParam represents a type parameter type.
+// A TypeParam represents the type of a type parameter in a generic declaration.
+//
+// A TypeParam has a name; use the [TypeParam.Obj] method to access
+// its [TypeName] object.
type TypeParam struct {
check *Checker // for lazy type bound completion
id uint64 // unique id, for debugging only
)
// An Alias represents an alias type.
-// Whether or not Alias types are created is controlled by the
-// gotypesalias setting with the GODEBUG environment variable.
-// For gotypesalias=1, alias declarations produce an Alias type.
-// Otherwise, the alias information is only in the type name,
-// which points directly to the actual (aliased) type.
+//
+// Alias types are created by alias declarations such as:
+//
+// type A = int
+//
+// The type on the right-hand side of the declaration can be accessed
+// using [Alias.Rhs]. This type may itself be an alias.
+// Call [Unalias] to obtain the first non-alias type in a chain of
+// alias type declarations.
+//
+// Like a defined ([Named]) type, an alias type has a name.
+// Use the [Alias.Obj] method to access its [TypeName] object.
+//
+// Historically, Alias types were not materialized so that, in the example
+// above, A's type was represented by a Basic (int), not an Alias
+// whose [Alias.Rhs] is int. But Go 1.24 allows you to declare an
+// alias type with type parameters or arguments:
+//
+// type Set[K comparable] = map[K]bool
+// s := make(Set[String])
+//
+// and this requires that Alias types be materialized. Use the
+// [Alias.TypeParams] and [Alias.TypeArgs] methods to access them.
+//
+// To ease the transition, the Alias type was introduced in go1.22,
+// but the type-checker would not construct values of this type unless
+// the GODEBUG=gotypesalias=1 environment variable was provided.
+// Starting in go1.23, this variable is enabled by default.
+// This setting also causes the predeclared type "any" to be
+// represented as an Alias, not a bare [Interface].
type Alias struct {
obj *TypeName // corresponding declared alias object
orig *Alias // original, uninstantiated alias
// in its "lineage".
// A Named represents a named (defined) type.
+//
+// A declaration such as:
+//
+// type S struct { ... }
+//
+// creates a defined type whose underlying type is a struct,
+// and binds this type to the object S, a [TypeName].
+// Use [Named.Underlying] to access the underlying type.
+// Use [Named.Obj] to obtain the object S.
+//
+// Before type aliases (Go 1.9), the spec called defined types "named types".
type Named struct {
check *Checker // non-nil during type-checking; nil otherwise
obj *TypeName // corresponding declared object for declared types; see above for instantiated types
"unicode/utf8"
)
-// An Object describes a named language entity such as a package,
-// constant, type, variable, function (incl. methods), or label.
-// All objects implement the Object interface.
+// An Object is a named language entity.
+// An Object may be a constant ([Const]), type name ([TypeName]),
+// variable or struct field ([Var]), function or method ([Func]),
+// imported package ([PkgName]), label ([Label]),
+// built-in function ([Builtin]),
+// or the predeclared identifier 'nil' ([Nil]).
+//
+// The environment, which is structured as a tree of Scopes,
+// maps each name to the unique Object that it denotes.
type Object interface {
Parent() *Scope // scope in which this object is declared; nil for methods and struct fields
Pos() token.Pos // position of object identifier in declaration
Id() string // object name if exported, qualified name if not exported (see func Id)
// String returns a human-readable string of the object.
+ // Use [ObjectString] to control how package names are formatted in the string.
String() string
// order reflects a package-level object's source order: if object
func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
-// A TypeName represents a name for a (defined or alias) type.
+// A TypeName is an [Object] that represents a type with a name:
+// a defined type ([Named]),
+// an alias type ([Alias]),
+// a type parameter ([TypeParam]),
+// or a predeclared type such as int or error.
type TypeName struct {
object
}
// each call, starting with 1. It may be called concurrently.
func nextID() uint64 { return uint64(lastID.Add(1)) }
-// A TypeParam represents a type parameter type.
+// A TypeParam represents the type of a type parameter in a generic declaration.
+//
+// A TypeParam has a name; use the [TypeParam.Obj] method to access
+// its [TypeName] object.
type TypeParam struct {
check *Checker // for lazy type bound completion
id uint64 // unique id, for debugging only