| // Copyright 2021 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package types2 |
| |
| import ( |
| "cmd/compile/internal/syntax" |
| "fmt" |
| ) |
| |
| // Instantiate instantiates the type typ with the given type arguments. |
| // typ must be a *Named or a *Signature type, it must be generic, and |
| // its number of type parameters must match the number of provided type |
| // arguments. The result is a new, instantiated (not generic) type of |
| // the same kind (either a *Named or a *Signature). The type arguments |
| // are not checked against the constraints of the type parameters. |
| // Any methods attached to a *Named are simply copied; they are not |
| // instantiated. |
| func Instantiate(pos syntax.Pos, typ Type, targs []Type) (res Type) { |
| // TODO(gri) This code is basically identical to the prolog |
| // in Checker.instantiate. Factor. |
| var tparams []*TypeName |
| switch t := typ.(type) { |
| case *Named: |
| tparams = t.tparams |
| case *Signature: |
| tparams = t.tparams |
| defer func() { |
| // If we had an unexpected failure somewhere don't panic below when |
| // asserting res.(*Signature). Check for *Signature in case Typ[Invalid] |
| // is returned. |
| if _, ok := res.(*Signature); !ok { |
| return |
| } |
| // If the signature doesn't use its type parameters, subst |
| // will not make a copy. In that case, make a copy now (so |
| // we can set tparams to nil w/o causing side-effects). |
| if t == res { |
| copy := *t |
| res = © |
| } |
| // After instantiating a generic signature, it is not generic |
| // anymore; we need to set tparams to nil. |
| res.(*Signature).tparams = nil |
| }() |
| |
| default: |
| panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ)) |
| } |
| |
| // the number of supplied types must match the number of type parameters |
| if len(targs) != len(tparams) { |
| panic(fmt.Sprintf("%v: got %d arguments but %d type parameters", pos, len(targs), len(tparams))) |
| } |
| |
| if len(tparams) == 0 { |
| return typ // nothing to do (minor optimization) |
| } |
| |
| smap := makeSubstMap(tparams, targs) |
| return (*Checker)(nil).subst(pos, typ, smap) |
| } |