introduce overload class

and use it with std::visit when inspecting std::alternative

1 files changed, 19 insertions, 0 deletions

diff --git a/vespalib/src/tests/overload/overload_test.cpp b/vespalib/src/tests/overload/overload_test.cpp
new file mode 100644
index 00000000000..ceae29ac02f
--- /dev/null
+++ b/vespalib/src/tests/overload/overload_test.cpp
@@ -0,0 +1,19 @@
+// Copyright 2020 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#include <vespa/vespalib/util/overload.h>
+#include <vespa/vespalib/gtest/gtest.h>
+#include <variant>
+#include <string>
+
+using namespace vespalib;
+
+TEST(OverloadTest, visit_with_overload_works) {
+    std::variant<std::string,int> a = 10;
+    std::variant<std::string,int> b = "foo";
+    std::visit(overload{[](int v){ EXPECT_EQ(v,10); },
+                        [](const std::string &){ FAIL() << "invalid visit"; }}, a);
+    std::visit(overload{[](int){ FAIL() << "invalid visit"; },
+                        [](const std::string &v){ EXPECT_EQ(v, "foo"); }}, b);
+}
+
+GTEST_MAIN_RUN_ALL_TESTS()