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-rw-r--r--src/development/c++/fwd.cc58
1 files changed, 58 insertions, 0 deletions
diff --git a/src/development/c++/fwd.cc b/src/development/c++/fwd.cc
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+++ b/src/development/c++/fwd.cc
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+// Copyright (C) 2023 johannst
+
+#include <cstdio>
+#include <utility>
+
+struct M {};
+
+// -- CONSUMER -----------------------------------------------------------------
+
+void use(M&) {
+ puts(__PRETTY_FUNCTION__);
+}
+
+void use(M&&) {
+ puts(__PRETTY_FUNCTION__);
+}
+
+// -- TESTER -------------------------------------------------------------------
+
+template<typename T>
+void wrapper(T&& param) { // forwarding reference
+ puts(__PRETTY_FUNCTION__);
+ // PARAM is an lvalue, therefore this always calls use(M&).
+ use(param);
+}
+
+template<typename T>
+void fwd_wrapper(T&& param) { // forwarding reference
+ puts(__PRETTY_FUNCTION__);
+ // PARAM is an lvalue, but std::forward returns PARAM with the same value
+ // category as the forwarding reference takes.
+ use(std::forward<T>(param));
+}
+
+// -- MAIN ---------------------------------------------------------------------
+
+int main() {
+ {
+ std::puts("==> wrapper rvalue reference");
+ wrapper(M{});
+ // calls use(M&).
+
+ std::puts("==> wrapper lvalue reference");
+ struct M m;
+ wrapper(m);
+ // calls use(M&).
+ }
+ {
+ std::puts("==> fwd_wrapper rvalue reference");
+ fwd_wrapper(M{});
+ // calls use(M&&).
+
+ std::puts("==> fwd_wrapper lvalue reference");
+ struct M m;
+ fwd_wrapper(m);
+ // calls use(M&).
+ }
+}