conditionalfunctor.md

Conditional functor reference

Description

The header file eventpp/utilities/conditionalfunctor.h contains utilities that can check certain condition then decide whether to invoke the underlying function.

For example,

eventpp::CallbackList<void(int)> callbackList;

callbackList.append(
    eventpp::conditionalFunctor(
        [](const int value) {
            std::cout << "We should get value 1." << here;
        },
        [](const int value) {
            return value == 1;
        }
    )
);
callbackList(2); // not trigger the callback
callbackList(1); // trigger the callback

Header

eventpp/utilities/conditionalfunctor.h

API reference

template <typename Func, typename Condition>
ConditionalFunctor<Func, Condition> conditionalFunctor(Func func, Condition condition);

Function conditionalFunctor receives a function func, and a conditional function condition, and return a functor object of ConditionalFunctor. ConditionalFunctor has a function invoking operator that forwards all arguments to condition, if condition returns true, func will be invoked with same arguments, if condition return false, func will not be invoked. The return value of conditionalFunctor can be passed to CallbackList, EventDispatcher, or EventQueue.

Below is the example code to demonstrate how to use conditionalFunctor, it's grabbed from the unit tests.

eventpp::CallbackList<void(int)> callbackList;

std::vector<int> dataList(3);
callbackList.append(
    eventpp::conditionalFunctor(
        [&dataList](const int index) {
            ++dataList[index];
        },
        [](const int index) {
            return index == 0;
        }
    )
);
callbackList.append(
    eventpp::conditionalFunctor(
        [&dataList](const int index) {
            ++dataList[index];
        },
        [](const int index) {
            return index == 1;
        }
    )
);
callbackList.append(
    eventpp::conditionalFunctor(
        [&dataList](const int index) {
            ++dataList[index];
        },
        [](const int index) {
            return index == 2;
        }
    )
);

REQUIRE(dataList == std::vector<int>{ 0, 0, 0 });

callbackList(2);
REQUIRE(dataList == std::vector<int>{ 0, 0, 1 });

callbackList(0);
REQUIRE(dataList == std::vector<int>{ 1, 0, 1 });

callbackList(1);
REQUIRE(dataList == std::vector<int>{ 1, 1, 1 });