Урок 10 variadic templates 2/3

kutuzzzov

Jul 19th, 2023

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#include <cassert>
#include <memory>
#include <string>
// Шаблон ApplyToMany применяет функцию f (первый аргумент) последовательно к каждому из остальных своих аргументов
template <typename f, typename... Vs>
void ApplyToMany(f& func, Vs&&... vs) {
(..., func(std::forward <Vs>(vs)));
}
void TestSum() {
int x;
auto lambda = [&x](int y) {
x += y;
};
x = 0;
ApplyToMany(lambda, 1);
assert(x == 1);
x = 0;
ApplyToMany(lambda, 1, 2, 3, 4, 5);
assert(x == 15);
}
void TestConcatenate() {
using namespace std::literals;
std::string s;
auto lambda = [&s](const auto& t) {
if (!s.empty()) {
s += " ";
}
s += t;
};
ApplyToMany(lambda, "cyan"s, "magenta"s, "yellow"s, "black"s);
assert(s == "cyan magenta yellow black"s);
}
void TestIncrement() {
auto increment = [](int& x) {
++x;
};
int a = 0;
int b = 3;
int c = 43;
ApplyToMany(increment, a, b, c);
assert(a == 1);
assert(b == 4);
assert(c == 44);
}
void TestArgumentForwarding() {
struct S {
int call_count = 0;
int i = 0;
std::unique_ptr<int> p;
void operator()(int i) {
this->i = i;
++call_count;
}
void operator()(std::unique_ptr<int>&& p) {
this->p = std::move(p);
++call_count;
}
};
S s;
ApplyToMany(s, 1, std::make_unique<int>(42));
assert(s.call_count == 2);
assert(s.i == 1);
assert(s.p != nullptr && *s.p == 42);
}
void TestArgumentForwardingToConstFunction() {
struct S {
mutable int call_count = 0;
mutable int i = 0;
mutable std::unique_ptr<int> p;
void operator()(int i) const {
this->i = i;
++call_count;
}
void operator()(std::unique_ptr<int>&& p) const {
this->p = std::move(p);
++call_count;
}
};
const S s;
ApplyToMany(s, 1, std::make_unique<int>(42));
assert(s.call_count == 2);
assert(s.i == 1);
assert(s.p != nullptr && *s.p == 42);
}
int main() {
TestSum();
TestConcatenate();
TestIncrement();
TestArgumentForwarding();
TestArgumentForwardingToConstFunction();
return 0;
}

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