#include <iostream>
#include <utility>
 
template <typename T, typename = size_t>
struct HasField_abc : std::false_type { };
 
template <typename T>
struct HasField_abc<T, decltype(sizeof(std::declval<T>().abc))> : std::true_type { };
 
template <typename T>
std::enable_if_t<HasField_abc<T>::value> get(T&)
{
	std::cout << "Has abc" << std::endl;
	// . . .
}
 
template <typename T>
std::enable_if_t<!HasField_abc<T>::value> get(T&)
{
	std::cout << "Has no abc" << std::endl;
	// . . .
}
 
struct Foo
{
	std::string abc;
};
 
struct Bar
{
	std::string ab;
};
 
int main()
{
	Foo foo;
	get(foo); // Has abc
 
	Bar bar;
	get(bar); // Has no abc
 
	int i;
	get(i); // Has no abc
}

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