add the actual example code

Author: dietmarkuehl

examples/when-all.cpp

@@ -0,0 +1,22 @@
+// examples/when-all.cpp                                              -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/task.hpp>
+#include <beman/execution/execution.hpp>
+#include <concepts>
+
+namespace ex = beman::execution;
+
+// ----------------------------------------------------------------------------
+
+int main() {
+    ex::sync_wait([]()->ex::task<>{
+        [[maybe_unused]] auto s = ex::when_all(
+            ex::just(true),
+            ex::just(10)
+            );
+        //static_assert(std::same_as<void, decltype(ex::get_completion_signatures(s, ex::empty_env{}))>);
+        co_await std::move(s);
+        co_return;
+        }());
+}