From d7725b45bfd33163840536f975853837aa8e4763 Mon Sep 17 00:00:00 2001 From: Kitsune Ral Date: Mon, 2 Apr 2018 14:13:11 +0900 Subject: 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. --- lib/util.h | 178 ++++++------------------------------------------------------- 1 file 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 #include +#include 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. lookup(parameters...)). 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 const char* selector - * (the first parameter) - most likely it won't do what you expect because - * of shallow comparison. - */ - template - ValueT lookup(SelectorT/*unused*/, ValueT&& fallback) - { - return std::forward(fallback); - } - - template - ValueT lookup(SelectorT&& selector, KeyT&& key, ValueT&& value, Ts&&... remainder) - { - if( selector == key ) - return std::forward(value); - - // Drop the failed key-value pair and recurse with 2 arguments less. - return lookup(std::forward(selector), - std::forward(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, 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 -#else - template -#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; - explicit Dispatch(ArgT&& arg) - : boundArgs([=](fn_t &&f) { return f(std::move(arg)); }) - { } -#else - using fn_t = std::function; - explicit Dispatch(ArgTs&&... args) - : boundArgs([=](fn_t &&f) { return f(std::move(args)...); }) - { } -#endif - - template - 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(std::forward(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 boundArgs; - }; - - /** - * Dispatch a set of parameters to one of a set of functions, depending on - * a selector value - * - * Use dispatch(parameters).to(lookup parameters) - * 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 - Dispatch dispatch(ArgTs&& ... args) - { - return Dispatch(std::forward(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 + inline auto unique_ptr_cast(PtrT2&& p) + { + return std::unique_ptr(static_cast(p.release())); + } + +#if QT_VERSION < QT_VERSION_CHECK(5, 7, 0) + // Copy-pasted from Qt 5.10 + template + Q_DECL_CONSTEXPR typename std::add_const::type &qAsConst(T &t) Q_DECL_NOTHROW { return t; } + // prevent rvalue arguments: + template + static void qAsConst(const T &&) Q_DECL_EQ_DELETE; +#endif } // namespace QMatrixClient -- cgit v1.2.3