(Optional) C++ - Lambda Expressions

Introduction

Recursive Lambdas

With y_combinator

If we add the following from the link above in C++14:

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namespace std {

template <class Fun> class y_combinator_result {
	Fun fun_;

  public:
	template <class T>
	explicit y_combinator_result(T &&fun) : fun_(std::forward<T>(fun)) {}

	template <class... Args> decltype(auto) operator()(Args &&...args) {

Then we can have code like the following:

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int main() {
	cout << y_combinator([](auto gcd, int a, int b) -> int {
		return b == 0 ? a : gcd(b, a % b);
	})(20, 30)
	     << "\n";  // outputs 10
}

With function

Instead of auto, use function<return_type(param)>.

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int main() {
	function<int(int, int)> gcd = [&](int a, int b) {
		return b == 0 ? a : gcd(b, a % b);
	};
	cout << gcd(20, 30) << '\n';  // outputs 10
}