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qfunctionutils.hpp
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qfunctionutils.hpp
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/*
* This file is part of kazv.
* SPDX-FileCopyrightText: 2019 juangburgos <https://github.com/juangburgos/>
* SPDX-License-Identifier: MIT
*/
/// https://github.com/juangburgos/QFunctionUtils/blob/master/src/qfunctionutils.h
#pragma once
#include <libkazv-config.hpp>
#include <functional>
#include <QSharedPointer>
#include <QTimer>
namespace QFunctionUtils
{
// function used to cache user arguments to be able to use them once timer times out
template<typename R, class ...Args>
void debounce_args_cache(const std::function<R(Args(...args))> &funcFinish, Args(&...args))
{
funcFinish(args...);
}
typedef QSharedPointer<QMetaObject::Connection> QMetaConnPtr;
// debounce implementation
// gets a user defined function as an argument and a 'delay' in miliseconds
// returns a new function that the user can call many times, but will only execute the last
// call after 'delay' miliseconds have passed
template<typename R, class ...Args>
std::function<R(Args(...args))> debounce_internal(const std::function<R(Args(...args))> &callback, const int &delay)
{
QTimer * timer = new QTimer;
QMetaConnPtr conn = QMetaConnPtr(new QMetaObject::Connection,
[timer](QMetaObject::Connection * pConn) mutable {
// connection will be deleted when returned function goes out of scope, but not the timer
// so we need to delete it manually
delete pConn;
delete timer;
});
timer->setInterval(delay);
// return function that the user can call
return [callback, timer, conn](Args(...args)) {
// disconnect old timer callback, stop timer
QObject::disconnect(*conn);
timer->stop();
// create function that caches user arguments
std::function<void(std::function<R(Args(...args))>)> funcCache = std::bind(debounce_args_cache<R, Args...>, std::placeholders::_1, args...);
// connect new timer callback, restart timer
*conn = QObject::connect(timer, &QTimer::timeout,
[callback, timer, funcCache]() {
// stop timer
timer->stop();
// call after delay
funcCache(callback);
});
timer->start();
// return default constructed return type (just to support any return type)
return R();
};
}
// throttle implementation
// same as debounce, but also calls the given function the first time is called
template<typename R, class ...Args>
std::function<R(Args(...args))> throttle_internal(const std::function<R(Args(...args))> &callback, const int &delay)
{
QTimer * timer = new QTimer;
QMetaConnPtr conn = QMetaConnPtr(new QMetaObject::Connection,
[timer](QMetaObject::Connection * pConn) mutable {
// same logic as in debounce_internal
delete pConn;
delete timer;
});
timer->setInterval(delay);
// return function that the user can call
return [callback, timer, conn](Args(...args)) {
// disconnect old timer callback
QObject::disconnect(*conn);
// check timer (throttle) state
if (!timer->isActive())
{
// connect new timer callback
*conn = QObject::connect(timer, &QTimer::timeout,
[timer]() {
// stop timer only (this happens if user did not call the function during the delay)
timer->stop();
});
// start timer to start throttle
timer->start();
// call inmediatly and return
return callback(args...);
}
// create function that caches user arguments
std::function<void(std::function<R(Args(...args))>)> funcCache = std::bind(debounce_args_cache<R, Args...>, std::placeholders::_1, args...);
// connect new timer callback
*conn = QObject::connect(timer, &QTimer::timeout,
[callback, timer, funcCache]() {
// stop timer
timer->stop();
// call after delay
funcCache(callback);
});
// return default constructed return type (just to support any return type)
return R();
};
}
// for any class implementing operator() (e.g. lambdas)
template<typename T> struct functor_traits : functor_traits<decltype(&T::operator())>
{ };
// specialization - lambda
template<typename C, typename R, typename... Args>
struct functor_traits<R(C::*)(Args...) const>
{
using lambda_type = std::function<R(Args...)>;
};
// specialization - lambda mutable
template<typename C, typename R, typename... Args>
struct functor_traits<R(C::*)(Args...)>
{
using lambda_type = std::function<R(Args...)>;
};
// specialization - function pointer
template<class R, class... Args>
struct functor_traits<R(*)(Args...)>
{
using lambda_type = std::function<R(Args...)>;
};
// wrap any of the specializations above into an std::function
template<typename T>
auto make_std_function(const T& fn) -> typename functor_traits<T>::lambda_type
{
return typename functor_traits<T>::lambda_type(fn);
}
// convert callback into std::function and call internal debounce
template<typename T>
auto Debounce(T callback, const int &delay) -> typename functor_traits<T>::lambda_type
{
return debounce_internal(make_std_function(callback), delay);
}
// convert callback into std::function and call internal throttle
template<typename T>
auto Throttle(T callback, const int &delay) -> typename functor_traits<T>::lambda_type
{
return throttle_internal(make_std_function(callback), delay);
}
}

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