I want to declare a function while setting the value of a function pointer.
A TypeScript equivalent:
let fp: () => void;
fp = () => {
console.log("Hello from inline function declaration!");
};
I've tried looking online but I can't seem to find anything that is related to what I'm looking for. I don't think this is possible but if it was it would be very helpful for a project I'm working on. I know this may be a stupid question but I really would like to know the answer.
A lambda without state can be converted to a function pointer. You can even force the conversion by using the unary + operator, as in
auto lambda = []() { do_something(); };
auto function_ptr = +[]() { do_something(); };
but normal implicit casting also works.
So this is roughly what you want.
#include <iostream>
int main()
{
void (*fp)() = nullptr;
fp = []() {
std::clog << "Hello from inline function declaration!\n";
};
fp();
}
extern void (*fp)(); is also redundant in C++, although it would usually be placed in a header to share it with other translation units that don't know about the definition in the following line.
extern, and you can move the lambda into main(). That may be closer to the OP's use-case, eg: void (*fp)() = nullptr; ... int main() { fp = []() { ... }; ... fp(); }
std::function and a lambda expression will basically let you have this syntax
std::function<void()> fp;
fp = [](){ console.log("Hello from inline function declaration!"); };
std::function does use type erasure so there is an overhead cost over a raw function pointer but this will let you use stateful functors as well.
