go source for verification 2026-05-22

test/typeswitch2.go

@@ -0,0 +1,37 @@
+// errorcheck
+
+// Copyright 2009 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.
+
+// Verify that various erroneous type switches are caught by the compiler.
+// Does not compile.
+
+package main
+
+import "io"
+
+func whatis(x interface{}) string {
+	switch x.(type) {
+	case int:
+		return "int"
+	case int: // ERROR "duplicate"
+		return "int8"
+	case io.Reader:
+		return "Reader1"
+	case io.Reader: // ERROR "duplicate"
+		return "Reader2"
+	case interface {
+		r()
+		w()
+	}:
+		return "rw"
+	case interface {	// ERROR "duplicate"
+		w()
+		r()
+	}:
+		return "wr"
+
+	}
+	return ""
+}