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/* the goal was to make reusable functions that behave like python decorator functions

* e.g. decorators wrap existing functions and return aggregate function

* auto foo = exception_fail_safe(fileread("missing_file.txt"));

* foo(); // works!

* auto bar = output_result(foo); // further decoration

* bar(); // output: "Exception caught: missing_file.txt not found!"

* Play with source at https://godbolt.org/z/jflOuu

* View the tutorial at https://github.com/TheMaverickProgrammer/C-Python-like-Decorators

#include <iostream>

#include <memory>

#include <cassert>

using namespace std;

/////////////////////////

// decorators //

/////////////////////////

template<typename F>

constexpr auto stars(const F& func) {

return [func](auto&&... args) {

cout << "*******" << endl;

func(forward<decltype(args)>(args)...);

cout << "\n*******" << endl;

};

}

template<typename F>

constexpr auto smart_divide(const F& func) {

return [func](float a, float b) {

cout << "I am going to divide a=" << a << " and b=" << b << endl;

if(b == 0) {

cout << "Whoops! cannot divide" << endl;

return 0.0f;

}

return func(a, b);

};

}

template<typename F>

constexpr auto output(const F& func) {

return [func](auto&&... args) {

cout << func(forward<decltype(args)>(args)...);

};

}

////////////////////////////////////////

// function implementations //

////////////////////////////////////////

void hello_impl() {

cout << "hello, world!";

}

float divide_impl(float a, float b) {

return a/b;

}

/////////////////////////////////////////

// final decorated functions //

/////////////////////////////////////////

constexpr auto hello = stars(hello_impl);

constexpr auto divide = stars(output(smart_divide(divide_impl)));

constexpr auto print = stars(printf);

// example for declaring a decorated function in one step.

// foo() cannot be templated for now, but C++20 should make this possible

constexpr auto foo = stars(

[](unsigned n=10) {

for (unsigned i = 0; i < n; ++i)

cout << "FOO!\n";

}

);

int main() {

hello();

divide(12.0f, 3.0f);

print("C++ is %s!", "epic!");

foo(3);

return 0;

}

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