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go/types: added another example to examples/types.go2 

Also: disabled aggressive rewriting of methods upon type instantiation

(Need to first figure out what we really need to do.)

Change-Id: I6fba78d60963534ebfe130164058ac1fbed7e5a3
This commit is contained in:
Robert Griesemer 2019-11-27 16:06:14 -08:00
parent 47ddbd09af
commit 45eb8a74f0
2 changed files with 29 additions and 9 deletions
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18
src/go/types/examples/types.go2
View File

@ -81,3 +81,21 @@ func _() {
x1a = x2a // ERROR assignment
x1a.f = x2a.f
}
// Another interesting corner case is parameterized types that don't use
// their type arguments. For instance:
type T(type P) struct{}
var xint T(int)
var xbool T(bool)
// Are these two variables of the same type? After all, their underlying
// types are identical. We consider them to be different because each type
// instantiation creates a new named type, in this case T<int> and T<bool>
// even if their underlying types are identical. This is sensible because
// we might still have methods that have different signatures or behave
// differently depending on the type arguments, and thus we can't possibly
// consider such types identical. Consequently:
func _() {
xint = xbool // ERROR assignment
}

20
src/go/types/subst.go
View File

@ -194,16 +194,18 @@ func (subst *subster) typ(typ Type) Type {
dump(">>> subst %s(%s) with %s (new: %s)", t.underlying, subst.tpars, subst.targs, new_targs)
named.underlying = subst.typ(t.underlying)
named.methods = t.methods // for now
// TODO(gri) how much work do we really need to do here?
// instantiate custom methods as necessary
for _, m := range t.methods {
// methods may not have a fully set up signature yet
dump(">>> instantiate %s", m)
subst.check.objDecl(m, nil)
sig := subst.check.subst(m.pos, m.typ, subst.tpars /*m.tparams*/, subst.targs).(*Signature)
m1 := NewFunc(m.pos, m.pkg, m.name, sig)
dump(">>> %s: method %s => %s", name, m, m1)
named.methods = append(named.methods, m1)
}
// for _, m := range t.methods {
// // methods may not have a fully set up signature yet
// dump(">>> instantiate %s", m)
// subst.check.objDecl(m, nil)
// sig := subst.check.subst(m.pos, m.typ, subst.tpars /*m.tparams*/, subst.targs).(*Signature)
// m1 := NewFunc(m.pos, m.pkg, m.name, sig)
// dump(">>> %s: method %s => %s", name, m, m1)
// named.methods = append(named.methods, m1)
// }
// TODO(gri) update the method receivers?
return named