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gchudnov/cpp_call_once.cpp

Created November 6, 2014 19:39
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Lazy (call once)
Raw
cpp_call_once.cpp
#include <iostream>
#include <memory>
#include <functional>
#include <mutex>
template <typename T>
struct lazy {
public:
template <typename Fun>
explicit lazy(Fun&& fun) : fun(std::forward<Fun>(fun)) {}
T& get() const {
std::call_once(flag, [this] { ptr.reset(fun()); });
return *ptr;
}
private:
std::once_flag flag;
std::unique_ptr<T> ptr;
std::function<T*()> fun;
};
class foo {};
int main() {
lazy<foo> x([] { return new foo; });
return 0;
}
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