id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
9223	Alllow find(key) with key's type different from the contained value type.	mjklaim@…	Ion Gaztañaga	"In a test, I have this:

{{{


struct Id
{
	int value;
};

bool operator==( const Id& a, const Id& b )
{
	return a.value == b.value;
}

bool operator< ( const Id& a, const Id& b )
{
	return a.value < b.value;
}


struct Event
{
	Id id;
	std::string data;
};

bool operator==( const Entity& a, const Entity& b )
{
	return a.id == b.id;
}

bool operator< ( const Entity& a, const Entity& b )
{
	return a.id < b.id;
}

bool operator==( const Id& a, const Entity& b )
{
	return a == b.id;
}
bool operator==( const Entity& a, const Id& b )
{
	return b == a;
}
}}}


Here value type Event can be compared to Id.
Now this test can't work:


{{{
boost::container::flat_set<Event> events;
events.find( Id{42} ); // ERROR: Id isn't an Event!

}}}


I would like this to compile because it would allow me to have a set of objects containing a state which can be overridden. In this test Event's value is it's id, but it contain associated data too which are not part of the comparison and can change when we insert new Events with the same id but different data.

This feature looks like a recent c++ proposal: n3573"	Feature Requests	closed	To Be Determined	container	Boost 1.54.0	Problem	fixed