Lambdas and Callables

Function Callbacks

std::function can store a callable and pass it to another function.

callback A callback is a callable passed to another function so that function can call it later.

Function Callbacks

count
function_callbacks.cpp
Replay: real traced execution (multi-file project)
#include <functional>
#include <iostream>

void repeat(int count, const std::function<void(int)>& callback) {
    for (int index = 1; index <= count; index++) {
        callback(index);
    }
}

int main() {
    int count = 3;
    int total = 0;

    repeat(count, [&total](int index) {
        total += index;
    });

    std::cout << "total=" << total << std::endl;
    std::cout << "done=" << count << std::endl;
    return 0;
}

#include <functional>
#include <iostream>

void repeat(int count, const std::function<void(int)>& callback) {
    for (int index = 1; index <= count; index++) {
        callback(index);
    }
}

int main() {
    int count = 1;
    int total = 0;

    repeat(count, [&total](int index) {
        total += index;
    });

    std::cout << "total=" << total << std::endl;
    std::cout << "done=" << count << std::endl;
    return 0;
}

#include <functional>
#include <iostream>

void repeat(int count, const std::function<void(int)>& callback) {
    for (int index = 1; index <= count; index++) {
        callback(index);
    }
}

int main() {
    int count = 4;
    int total = 0;

    repeat(count, [&total](int index) {
        total += index;
    });

    std::cout << "total=" << total << std::endl;
    std::cout << "done=" << count << std::endl;
    return 0;
}

  1. count ← 3, total ← 0

    10int main() {11    int count→ 3 = 3; //@count=1, 412    int total→ 0 = 0;1314    repeat(count3, [&total](int index) {15        total += index;16    });

  2. void repeat(int count, const std::function<void(int)>& callback)

    4void repeat(int count3, const std::function<void(int)>& callback(empty)) {5    for (int index = 1; index <= count; index++) {

  3. for (int index = 1; index <= count; index++)

    pass 1 of 3
    4void repeat(int count, const std::function<void(int)>& callback) {5    for (int index1 = 1; index <= count3; index++) {6        callback(empty)(index1);7    }
    All 3 passes — pass 1 is the card above
    passindex
    11
    22
    33

  4. repeat(count, [&total](int index)

    14    repeat(count3, [&total](int index) {15        total += index;16    });1718    std::cout << "total=" << total6 << std::endl;19    std::cout << "done=" << count3 << std::endl;20    return 0;21}
    outputtotal=6
done=3

  1. count ← 1, total ← 0

    10int main() {11    int count→ 1 = 1;12    int total→ 0 = 0;1314    repeat(count1, [&total](int index) {15        total += index;16    });

  2. void repeat(int count, const std::function<void(int)>& callback)

    4void repeat(int count1, const std::function<void(int)>& callback(empty)) {5    for (int index = 1; index <= count; index++) {

  3. for (int index = 1; index <= count; index++)

    4void repeat(int count, const std::function<void(int)>& callback) {5    for (int index1 = 1; index <= count1; index++) {6        callback(empty)(index1);7    }

  4. repeat(count, [&total](int index)

    14    repeat(count1, [&total](int index) {15        total += index;16    });1718    std::cout << "total=" << total1 << std::endl;19    std::cout << "done=" << count1 << std::endl;20    return 0;21}
    outputtotal=1
done=1

  1. count ← 4, total ← 0

    10int main() {11    int count→ 4 = 4;12    int total→ 0 = 0;1314    repeat(count4, [&total](int index) {15        total += index;16    });

  2. void repeat(int count, const std::function<void(int)>& callback)

    4void repeat(int count4, const std::function<void(int)>& callback(empty)) {5    for (int index = 1; index <= count; index++) {

  3. for (int index = 1; index <= count; index++)

    pass 1 of 4
    4void repeat(int count, const std::function<void(int)>& callback) {5    for (int index1 = 1; index <= count4; index++) {6        callback(empty)(index1);7    }
    All 4 passes — pass 1 is the card above
    passindex
    11
    22
    33
    44

  4. repeat(count, [&total](int index)

    14    repeat(count4, [&total](int index) {15        total += index;16    });1718    std::cout << "total=" << total10 << std::endl;19    std::cout << "done=" << count4 << std::endl;20    return 0;21}
    outputtotal=10
done=4