lookup()/dispatch() removed; unique_ptr_cast() and qAsConst() introduced

qAsConst() is a copy-paste from Qt code and is only supplied by QMatrixClient if Qt is below 5.7. unique_ptr_cast<> is similar to static_cast<> of pointers but deals with unique_ptr's, passing ownership to the newly made pointer.

1 files changed, 16 insertions, 162 deletions

diff --git a/lib/util.h b/lib/util.h
index 65de0610..92198b0b 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -22,171 +22,10 @@
 #include <QtCore/QDebug>
 
 #include <functional>
+#include <memory>
 
 namespace QMatrixClient
 {
-    /**
-     * @brief Lookup a value by a key in a varargs list
-     *
-     * This function template takes the value of its first argument (selector)
-     * as a key and searches for it in the key-value map passed in
-     * a parameter pack (every next pair of arguments forms a key-value pair).
-     * If a match is found, the respective value is returned; if no pairs
-     * matched, the last value (fallback) is returned.
-     *
-     * All options should be of the same type or implicitly castable to the
-     * type of the first option. If you need some specific type to cast to
-     * you can explicitly provide it as the ValueT template parameter
-     * (e.g. <code>lookup<void*>(parameters...)</code>). Note that pointers
-     * to methods of different classes and even to functions with different
-     * signatures are of different types. If their return types are castable
-     * to some common one, @see dispatch that deals with this by swallowing
-     * the method invocation.
-     *
-     * Below is an example of usage to select a parser depending on contents of
-     * a JSON object:
-     * {@code
-     *  auto parser = lookup(obj.value["type"].toString(),
-     *                      "type1", fn1,
-     *                      "type2", fn2,
-     *                      fallbackFn);
-     *  parser(obj);
-     * }
-     *
-     * The implementation is based on tail recursion; every recursion step
-     * removes 2 arguments (match and value). There's no selector value for the
-     * fallback option (the last one); therefore, the total number of lookup()
-     * arguments should be even: selector + n key-value pairs + fallback
-     *
-     * @note Beware of calling lookup() with a <code>const char*</code> selector
-     * (the first parameter) - most likely it won't do what you expect because
-     * of shallow comparison.
-     */
-    template <typename ValueT, typename SelectorT>
-    ValueT lookup(SelectorT/*unused*/, ValueT&& fallback)
-    {
-        return std::forward<ValueT>(fallback);
-    }
-
-    template <typename ValueT, typename SelectorT, typename KeyT, typename... Ts>
-    ValueT lookup(SelectorT&& selector, KeyT&& key, ValueT&& value, Ts&&... remainder)
-    {
-        if( selector == key )
-            return std::forward<ValueT>(value);
-
-        // Drop the failed key-value pair and recurse with 2 arguments less.
-        return lookup<ValueT>(std::forward<SelectorT>(selector),
-                              std::forward<Ts>(remainder)...);
-    }
-
-    /**
-     * A wrapper around lookup() for functions of different types castable
-     * to a common std::function<> form
-     *
-     * This class uses std::function<> magic to first capture arguments of
-     * a yet-unknown function or function object, and then to coerce types of
-     * all functions/function objects passed for lookup to the type
-     * std::function<ResultT(ArgTs...). Without Dispatch<>, you would have
-     * to pass the specific function type to lookup, since your functions have
-     * different signatures. The type is not always obvious, and the resulting
-     * construct in client code would almost always be rather cumbersome.
-     * Dispatch<> deduces the necessary function type (well, almost - you still
-     * have to specify the result type) and hides the clumsiness. For more
-     * information on what std::function<> can wrap around, see
-     * https://cpptruths.blogspot.jp/2015/11/covariance-and-contravariance-in-c.html
-     *
-     * The function arguments are captured by value (i.e. copied) to avoid
-     * hard-to-find issues with dangling references in cases when a Dispatch<>
-     * object is passed across different contexts (e.g. returned from another
-     * function).
-     *
-     * \tparam ResultT - the desired type of a picked function invocation (mandatory)
-     * \tparam ArgTs - function argument types (deduced)
-     */
-#if __GNUC__ < 5 && __GNUC_MINOR__ < 9
-    // GCC 4.8 cannot cope with parameter packs inside lambdas; so provide a single
-    // argument version of Dispatch<> that we only need so far.
-    template <typename ResultT, typename ArgT>
-#else
-    template <typename ResultT, typename... ArgTs>
-#endif
-    class Dispatch
-    {
-            // The implementation takes a chapter from functional programming:
-            // Dispatch<> uses a function that in turn accepts a function as its
-            // argument. The sole purpose of the outer function (initialized by
-            // a lambda-expression in the constructor) is to store the arguments
-            // to any of the functions later looked up. The inner function (its
-            // type is defined by fn_t alias) is the one returned by lookup()
-            // invocation inside to().
-            //
-            // It's a bit counterintuitive to specify function parameters before
-            // the list of functions but otherwise it would take several overloads
-            // here to match all the ways a function-like behaviour can be done:
-            // reference-to-function, pointer-to-function, function object. This
-            // probably could be done as well but I preferred a more compact
-            // solution: you show what you have and if it's possible to bring all
-            // your functions to the same std::function<> based on what you have
-            // as parameters, the code will compile. If it's not possible, modern
-            // compilers are already good enough at pinpointing a specific place
-            // where types don't match.
-        public:
-#if __GNUC__ < 5 && __GNUC_MINOR__ < 9
-            using fn_t = std::function<ResultT(ArgT)>;
-            explicit Dispatch(ArgT&& arg)
-                : boundArgs([=](fn_t &&f) { return f(std::move(arg)); })
-            { }
-#else
-            using fn_t = std::function<ResultT(ArgTs...)>;
-            explicit Dispatch(ArgTs&&... args)
-                : boundArgs([=](fn_t &&f) { return f(std::move(args)...); })
-            { }
-#endif
-
-            template <typename... LookupParamTs>
-            ResultT to(LookupParamTs&&... lookupParams)
-            {
-                // Here's the magic, two pieces of it:
-                // 1. Specifying fn_t in lookup() wraps all functions in
-                // \p lookupParams into the same std::function<> type. This
-                // includes conversion of return types from more specific to more
-                // generic (because std::function is covariant by return types and
-                // contravariant by argument types (see the link in the Doxygen
-                // part of the comments).
-                auto fn = lookup<fn_t>(std::forward<LookupParamTs>(lookupParams)...);
-                // 2. Passing the result of lookup() to boundArgs() invokes the
-                // lambda-expression mentioned in the constructor, which simply
-                // invokes this passed function with a set of arguments captured
-                // by lambda.
-                if (fn)
-                    return boundArgs(std::move(fn));
-
-                // A shortcut to allow passing nullptr for a function;
-                // a default-constructed ResultT will be returned
-                // (for pointers, it will be nullptr)
-                return {};
-            }
-
-        private:
-            std::function<ResultT(fn_t&&)> boundArgs;
-    };
-
-    /**
-     * Dispatch a set of parameters to one of a set of functions, depending on
-     * a selector value
-     *
-     * Use <code>dispatch<CommonType>(parameters).to(lookup parameters)</code>
-     * instead of lookup() if you need to pick one of several functions returning
-     * types castable to the same CommonType. See event.cpp for a typical use case.
-     *
-     * \see Dispatch
-     */
-    template <typename ResultT, typename... ArgTs>
-    Dispatch<ResultT, ArgTs...> dispatch(ArgTs&& ... args)
-    {
-        return Dispatch<ResultT, ArgTs...>(std::forward<ArgTs>(args)...);
-    }
-
     // The below enables pretty-printing of enums in logs
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 5, 0))
 #define REGISTER_ENUM(EnumName) Q_ENUM(EnumName)
@@ -201,5 +40,20 @@ namespace QMatrixClient
         return dbg << Event::staticMetaObject.enumerator(enumIdx).valueToKey(int(val)); \
     }
 #endif
+
+    template <typename T1, typename PtrT2>
+    inline auto unique_ptr_cast(PtrT2&& p)
+    {
+        return std::unique_ptr<T1>(static_cast<T1*>(p.release()));
+    }
+
+#if QT_VERSION < QT_VERSION_CHECK(5, 7, 0)
+    // Copy-pasted from Qt 5.10
+    template <typename T>
+    Q_DECL_CONSTEXPR typename std::add_const<T>::type &qAsConst(T &t) Q_DECL_NOTHROW { return t; }
+    // prevent rvalue arguments:
+    template <typename T>
+    static void qAsConst(const T &&) Q_DECL_EQ_DELETE;
+#endif
 }  // namespace QMatrixClient