1 files changed, 31 insertions, 0 deletions
diff --git a/vespalib/src/tests/explore_modern_cpp/explore_modern_cpp_test.cpp b/vespalib/src/tests/explore_modern_cpp/explore_modern_cpp_test.cpp
new file mode 100644
index 00000000000..05703b15641
--- /dev/null
+++ b/vespalib/src/tests/explore_modern_cpp/explore_modern_cpp_test.cpp
@@ -0,0 +1,31 @@
+// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+#include <vespa/vespalib/testkit/test_kit.h>
+
+TEST("verify how std::function copies lambda closures") {
+    size_t count = 0;
+    size_t value = 0;
+    auto closure = [count,&value]()mutable{ ++count; value += count; };
+    closure();
+    EXPECT_EQUAL(0u, count);
+    EXPECT_EQUAL(1u, value); // +1
+    closure();
+    EXPECT_EQUAL(3u, value); // +2
+    std::function<void()> fun = closure;
+    fun();
+    EXPECT_EQUAL(6u, value); // +3
+    closure();
+    EXPECT_EQUAL(9u, value); // +3 (fun had a copy of count)
+    auto &closure_ref = closure;
+    std::function<void()> fun2 = closure_ref;   
+    fun2();
+    EXPECT_EQUAL(13u, value); // +4
+    closure();
+    EXPECT_EQUAL(17u, value); // +4 (fun2 had a copy of count)
+    std::function<void()> fun3 = std::ref(closure);
+    fun3();
+    EXPECT_EQUAL(22u, value); // +5
+    closure();
+    EXPECT_EQUAL(28u, value); // +6 (fun only had a copy of the wrapper)
+}
+
+TEST_MAIN() { TEST_RUN_ALL(); }