Add aggregator macro.

src/alia/common.hpp

@@ -99,6 +99,15 @@ struct is_invocable
 #define alia_lambdify(f) ALIA_LAMBDIFY(f)
 #endif
 
+// ALIA_AGGREGATOR(f) produces a lambda that assembles its arguments into an
+// aggregate expression (i.e., "{args...}") and passes that into f.
+// This is useful, for example, when you want to explicitly refer to the
+// aggregate constructor of a type as an invocable function.
+#define ALIA_AGGREGATOR(f) [](auto&&... args) { return f{args...}; }
+#ifndef ALIA_STRICT_MACROS
+#define alia_aggregator(f) ALIA_AGGREGATOR(f)
+#endif
+
 // function_view is the non-owning equivalent of std::function.
 template<class Signature>
 class function_view;

unit_tests/common.cpp

@@ -12,6 +12,21 @@ TEST_CASE("exception", "[common]")
     REQUIRE(e.what() == std::string("just a test\nin here"));
 }
 
+struct aggregatable_struct
+{
+    int a;
+    std::string b;
+};
+
+TEST_CASE("ALIA_AGGREGATOR", "[common]")
+{
+    std::function<aggregatable_struct(int, std::string)> f;
+    f = ALIA_AGGREGATOR(aggregatable_struct);
+    auto x = f(4, "foo");
+    REQUIRE(x.a == 4);
+    REQUIRE(x.b == "foo");
+}
+
 int
 invoke_function_views(function_view<int(bool)> a, function_view<int(int)> b)
 {