reflect: add TypeFor

Fixes #60088

Change-Id: I7b43d329def22c2524501ba1d6bfc73becc823d1
GitHub-Last-Rev: becd714c45
GitHub-Pull-Request: golang/go#61598
Reviewed-on: https://go-review.googlesource.com/c/go/+/513478
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

api/next/60088.txt

@@ -0,0 +1 @@
+pkg reflect, func TypeFor[$0 interface{}]() Type #60088

src/reflect/type.go

@@ -2911,3 +2911,8 @@ func addTypeBits(bv *bitVector, offset uintptr, t *abi.Type) {
 		}
 	}
 }
+
+// TypeFor returns the [Type] that represents the type argument T.
+func TypeFor[T any]() Type {
+	return TypeOf((*T)(nil)).Elem()
+}

src/reflect/type_test.go

@@ -0,0 +1,35 @@
+// Copyright 2023 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 reflect_test
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestTypeFor(t *testing.T) {
+	type (
+		mystring string
+		myiface  interface{}
+	)
+
+	testcases := []struct {
+		wantFrom any
+		got      reflect.Type
+	}{
+		{new(int), reflect.TypeFor[int]()},
+		{new(int64), reflect.TypeFor[int64]()},
+		{new(string), reflect.TypeFor[string]()},
+		{new(mystring), reflect.TypeFor[mystring]()},
+		{new(any), reflect.TypeFor[any]()},
+		{new(myiface), reflect.TypeFor[myiface]()},
+	}
+	for _, tc := range testcases {
+		want := reflect.ValueOf(tc.wantFrom).Elem().Type()
+		if want != tc.got {
+			t.Errorf("unexpected reflect.Type: got %v; want %v", tc.got, want)
+		}
+	}
+}