funchelpers: Support the invocation of non-void callables

[quassel.git] / src / common / funchelpers.h

diff --git a/src/common/funchelpers.h b/src/common/funchelpers.h
index 01ee822..ede4e43 100644 (file)
--- a/src/common/funchelpers.h
+++ b/src/common/funchelpers.h
@@ -20,8 +20,19 @@
 
 #pragma once
 
+#include <array>
 #include <functional>
 #include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include <boost/optional.hpp>
+
+#include <QDebug>
+#include <QVariant>
+#include <QVariantList>
+
+// ---- Function traits --------------------------------------------------------------------------------------------------------------------
 
 namespace detail {
 
@@ -32,21 +43,27 @@ template<typename Func>
 struct FuncHelper : public FuncHelper<decltype(&Func::operator())>
 {};
 
-// Overload for member function with const call operator
-template<typename C, typename R, typename... Args>
-struct FuncHelper<R (C::*)(Args...) const> : public FuncHelper<R (C::*)(Args...)>
-{};
+// Overload for free function
+template<typename R, typename... Args>
+struct FuncHelper<R(*)(Args...)>
+{
+    using FunctionType = std::function<R(Args...)>;
+    using ReturnType = R;
+    using ArgsTuple = std::tuple<Args...>;
+};
 
 // Overload for member function with non-const call operator
 template<typename C, typename R, typename... Args>
-struct FuncHelper<R (C::*)(Args...)>
+struct FuncHelper<R(C::*)(Args...)> : public FuncHelper<R(*)(Args...)>
 {
     using ClassType = C;
-    using FunctionType = std::function<R(Args...)>;
-    using ReturnType = R;
-    using ArgsTuple = std::tuple<Args...>;
 };
 
+// Overload for member function with const call operator
+template<typename C, typename R, typename... Args>
+struct FuncHelper<R(C::*)(Args...) const> : public FuncHelper<R(C::*)(Args...)>
+{};
+
 /// @endcond
 
 }  // namespace detail
@@ -55,4 +72,71 @@ struct FuncHelper<R (C::*)(Args...)>
  * Provides traits for the given callable.
  */
 template<typename Callable>
-using MemberFunction = detail::FuncHelper<Callable>;
+using FunctionTraits = detail::FuncHelper<Callable>;
+
+// ---- Invoke function with argument list -------------------------------------------------------------------------------------------------
+
+namespace detail {
+
+// Helper for invoking the callable, wrapping its return value in a QVariant (default-constructed if callable returns void).
+// The correct overload is selected via SFINAE.
+template<typename Callable, typename ...Args>
+auto invokeWithArgs(const Callable& c, Args&&... args)
+    -> std::enable_if_t<std::is_void<typename FunctionTraits<Callable>::ReturnType>::value, QVariant>
+{
+    c(std::forward<Args>(args)...);
+    return QVariant{};
+}
+
+template<typename Callable, typename ...Args>
+auto invokeWithArgs(const Callable& c, Args&&... args)
+    -> std::enable_if_t<!std::is_void<typename FunctionTraits<Callable>::ReturnType>::value, QVariant>
+{
+    return QVariant::fromValue(c(std::forward<Args>(args)...));
+}
+
+// Helper for unpacking the argument list via an index sequence
+template<typename Callable, std::size_t ...Is, typename ArgsTuple = typename FunctionTraits<Callable>::ArgsTuple>
+boost::optional<QVariant> invokeWithArgsList(const Callable& c, const QVariantList& args, std::index_sequence<Is...>)
+{
+    // Sanity check that all types can be converted
+    std::array<bool, std::tuple_size<ArgsTuple>::value> convertible{{args[Is].canConvert<std::decay_t<std::tuple_element_t<Is, ArgsTuple>>>()...}};
+    for (size_t i = 0; i < convertible.size(); ++i) {
+        if (!convertible[i]) {
+            qWarning() << "Cannot convert parameter" << i << "from type" << args[static_cast<int>(i)].typeName() << "to expected argument type";
+            return boost::none;
+        }
+    }
+
+    // Invoke callable with unmarshalled arguments
+    return invokeWithArgs(c, args[Is].value<std::decay_t<std::tuple_element_t<Is, ArgsTuple>>>()...);
+}
+
+}  // detail
+
+/**
+ * Invokes the given callable with the arguments contained in the given variant list.
+ *
+ * The types contained in the given QVariantList are converted to the types expected by the callable.
+ * If the invocation is successful, the returned optional contains a QVariant with the return value,
+ * or an invalid QVariant if the callable returns void.
+ * If the conversion fails, or if the argument count does not match, this function returns boost::none
+ * and the callable is not invoked.
+ *
+ * @param c    Callable
+ * @param args Arguments to be given to the callable
+ * @returns An optional containing a QVariant with the return value if the callable could be invoked with
+ *          the given list of arguments; otherwise boost::none
+ */
+template<typename Callable>
+boost::optional<QVariant> invokeWithArgsList(const Callable& c, const QVariantList& args)
+{
+    using ArgsTuple = typename FunctionTraits<Callable>::ArgsTuple;
+    constexpr auto tupleSize = std::tuple_size<ArgsTuple>::value;
+
+    if (tupleSize != args.size()) {
+        qWarning().nospace() << "Argument count mismatch! Expected: " << tupleSize << ", actual: " << args.size();
+        return boost::none;
+    }
+    return detail::invokeWithArgsList(c, args, std::make_index_sequence<tupleSize>{});
+}