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package main
import "fmt"
func Fn[N any]() (any, any, any) {
// Very recursive type to exercise substitution.
type t[x any, ignored *N] struct {
f x
g N
nx *t[x, *N]
nn *t[N, *N]
}
n := t[N, *N]{}
s := t[string, *N]{}
i := t[int, *N]{}
return n, s, i
}
func main() {
sn, ss, si := Fn[string]()
in, is, ii := Fn[int]()
for i, t := range []struct {
x, y any
want bool
}{
{sn, ss, true}, // main.t[string;string,*string] == main.t[string;string,*string]
{sn, si, false}, // main.t[string;string,*string] != main.t[string;int,*string]
{sn, in, false}, // main.t[string;string,*string] != main.t[int;int,*int]
{sn, is, false}, // main.t[string;string,*string] != main.t[int;string,*int]
{sn, ii, false}, // main.t[string;string,*string] != main.t[int;int,*int]
{ss, si, false}, // main.t[string;string,*string] != main.t[string;int,*string]
{ss, in, false}, // main.t[string;string,*string] != main.t[int;int,*int]
{ss, is, false}, // main.t[string;string,*string] != main.t[int;string,*int]
{ss, ii, false}, // main.t[string;string,*string] != main.t[int;int,*int]
{si, in, false}, // main.t[string;int,*string] != main.t[int;int,*int]
{si, is, false}, // main.t[string;int,*string] != main.t[int;string,*int]
{si, ii, false}, // main.t[string;int,*string] != main.t[int;int,*int]
{in, is, false}, // main.t[int;int,*int] != main.t[int;string,*int]
{in, ii, true}, // main.t[int;int,*int] == main.t[int;int,*int]
{is, ii, false}, // main.t[int;string,*int] != main.t[int;int,*int]
} {
x, y, want := t.x, t.y, t.want
if got := x == y; got != want {
msg := fmt.Sprintf("(case %d) %T == %T. got %v. wanted %v", i, x, y, got, want)
panic(msg)
}
}
}
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