#include <vector>
#include <functional>
#include <iostream>
#include <string>

struct SomeClass
{
	int m_num;
};

std::function<void(SomeClass)> g_callback;

void CallbackBindTest(std::function<void(SomeClass)> a_callback)
{
	g_callback = a_callback;
}

int main()
{
	// no info about 'param' given here -
	// no auto-completed members, no type on hover.
	CallbackBindTest([](auto param) {
		std::cout << param.m_num << std::endl;
	});

	// invoke callback just to test (it will print '5')
	g_callback(SomeClass{ 5 });

	std::cin.get();
	return 0;
}

quote:

---

Originally posted by feline

This code compiles, but I am confused by how it works. I can follow that the template function takes the "SomeClass" type, but the lambda function does not seem to have any restriction on the types it can be called with. So what stops me calling the lambda with a different class type?

I am not following what limits / defines the type of the auto. I am seeing the same problem, I am just trying to work out if this is something that can be reasonably determined without compiling the code.

---

// invoke callback just to test (it will print '5')
	g_callback(SomeClass{ 5 });

	// fails - "cannot convert argument 1 from 'int' to 'SomeClass'"
	g_callback(5);