Documentation
¶
Overview ¶
Package typeparams contains common utilities for writing tools that interact with generic Go code, as introduced with Go 1.18. It supplements the standard library APIs. Notably, the StructuralTerms API computes a minimal representation of the structural restrictions on a type parameter.
An external version of these APIs is available in the golang.org/x/exp/typeparams module.
Index ¶
- Variables
- func CoreType(T types.Type) types.Type
- func Deref(t types.Type) types.Type
- func GenericAssignableTo(ctxt *types.Context, V, T types.Type) bool
- func InterfaceTermSet(iface *types.Interface) ([]*types.Term, error)
- func IsTypeParam(t types.Type) bool
- func MustDeref(t types.Type) types.Type
- func NormalTerms(typ types.Type) ([]*types.Term, error)
- func PackIndexExpr(x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) ast.Expr
- func StructuralTerms(tparam *types.TypeParam) ([]*types.Term, error)
- func UnionTermSet(union *types.Union) ([]*types.Term, error)
- func UnpackIndexExpr(n ast.Node) (x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos)
- type Free
Constants ¶
This section is empty.
Variables ¶
var ErrEmptyTypeSet = errors.New("empty type set")
Functions ¶
func CoreType ¶
CoreType returns the core type of T or nil if T does not have a core type.
See https://go.dev/ref/spec#Core_types for the definition of a core type.
func Deref ¶
Deref returns the type of the variable pointed to by t, if t's core type is a pointer; otherwise it returns t.
Do not assume that Deref(T)==T implies T is not a pointer: consider "type T *T", for example.
TODO(adonovan): ideally this would live in typesinternal, but that creates an import cycle. Move there when we melt this package down.
func GenericAssignableTo ¶
GenericAssignableTo is a generalization of types.AssignableTo that implements the following rule for uninstantiated generic types:
If V and T are generic named types, then V is considered assignable to T if, for every possible instantiation of V[A_1, ..., A_N], the instantiation T[A_1, ..., A_N] is valid and V[A_1, ..., A_N] implements T[A_1, ..., A_N].
If T has structural constraints, they must be satisfied by V.
For example, consider the following type declarations:
type Interface[T any] interface {
Accept(T)
}
type Container[T any] struct {
Element T
}
func (c Container[T]) Accept(t T) { c.Element = t }
In this case, GenericAssignableTo reports that instantiations of Container are assignable to the corresponding instantiation of Interface.
func InterfaceTermSet ¶
InterfaceTermSet computes the normalized terms for a constraint interface, returning an error if the term set cannot be computed or is empty. In the latter case, the error will be ErrEmptyTypeSet.
See the documentation of StructuralTerms for more information on normalization.
func IsTypeParam ¶
IsTypeParam reports whether t is a type parameter (or an alias of one).
func MustDeref ¶
MustDeref returns the type of the variable pointed to by t. It panics if t's core type is not a pointer.
TODO(adonovan): ideally this would live in typesinternal, but that creates an import cycle. Move there when we melt this package down.
func NormalTerms ¶
NormalTerms returns a slice of terms representing the normalized structural type restrictions of a type, if any.
For all types other than *types.TypeParam, *types.Interface, and *types.Union, this is just a single term with Tilde() == false and Type() == typ. For *types.TypeParam, *types.Interface, and *types.Union, see below.
Structural type restrictions of a type parameter are created via non-interface types embedded in its constraint interface (directly, or via a chain of interface embeddings). For example, in the declaration type T[P interface{~int; m()}] int the structural restriction of the type parameter P is ~int.
With interface embedding and unions, the specification of structural type restrictions may be arbitrarily complex. For example, consider the following:
type A interface{ ~string|~[]byte }
type B interface{ int|string }
type C interface { ~string|~int }
type T[P interface{ A|B; C }] int
In this example, the structural type restriction of P is ~string|int: A|B expands to ~string|~[]byte|int|string, which reduces to ~string|~[]byte|int, which when intersected with C (~string|~int) yields ~string|int.
NormalTerms computes these expansions and reductions, producing a "normalized" form of the embeddings. A structural restriction is normalized if it is a single union containing no interface terms, and is minimal in the sense that removing any term changes the set of types satisfying the constraint. It is left as a proof for the reader that, modulo sorting, there is exactly one such normalized form.
Because the minimal representation always takes this form, NormalTerms returns a slice of tilde terms corresponding to the terms of the union in the normalized structural restriction. An error is returned if the type is invalid, exceeds complexity bounds, or has an empty type set. In the latter case, NormalTerms returns ErrEmptyTypeSet.
NormalTerms makes no guarantees about the order of terms, except that it is deterministic.
func PackIndexExpr ¶
PackIndexExpr returns an *ast.IndexExpr or *ast.IndexListExpr, depending on the cardinality of indices. Calling PackIndexExpr with len(indices) == 0 will panic.
func StructuralTerms ¶
StructuralTerms returns a slice of terms representing the normalized structural type restrictions of a type parameter, if any.
Structural type restrictions of a type parameter are created via non-interface types embedded in its constraint interface (directly, or via a chain of interface embeddings). For example, in the declaration
type T[P interface{~int; m()}] int
the structural restriction of the type parameter P is ~int.
With interface embedding and unions, the specification of structural type restrictions may be arbitrarily complex. For example, consider the following:
type A interface{ ~string|~[]byte }
type B interface{ int|string }
type C interface { ~string|~int }
type T[P interface{ A|B; C }] int
In this example, the structural type restriction of P is ~string|int: A|B expands to ~string|~[]byte|int|string, which reduces to ~string|~[]byte|int, which when intersected with C (~string|~int) yields ~string|int.
StructuralTerms computes these expansions and reductions, producing a "normalized" form of the embeddings. A structural restriction is normalized if it is a single union containing no interface terms, and is minimal in the sense that removing any term changes the set of types satisfying the constraint. It is left as a proof for the reader that, modulo sorting, there is exactly one such normalized form.
Because the minimal representation always takes this form, StructuralTerms returns a slice of tilde terms corresponding to the terms of the union in the normalized structural restriction. An error is returned if the constraint interface is invalid, exceeds complexity bounds, or has an empty type set. In the latter case, StructuralTerms returns ErrEmptyTypeSet.
StructuralTerms makes no guarantees about the order of terms, except that it is deterministic.
func UnionTermSet ¶
UnionTermSet computes the normalized terms for a union, returning an error if the term set cannot be computed or is empty. In the latter case, the error will be ErrEmptyTypeSet.
See the documentation of StructuralTerms for more information on normalization.
func UnpackIndexExpr ¶
func UnpackIndexExpr(n ast.Node) (x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos)
UnpackIndexExpr extracts data from AST nodes that represent index expressions.
For an ast.IndexExpr, the resulting indices slice will contain exactly one index expression. For an ast.IndexListExpr (go1.18+), it may have a variable number of index expressions.
For nodes that don't represent index expressions, the first return value of UnpackIndexExpr will be nil.
Types ¶
type Free ¶
type Free struct {
// contains filtered or unexported fields
}
Free is a memoization of the set of free type parameters within a type. It makes a sequence of calls to Free.Has for overlapping types more efficient. The zero value is ready for use.
NOTE: Adapted from go/types/infer.go. If it is later exported, factor.
Source Files