Comparator for matching point in a range

Solution 1:

find returns an element that compares equivalent to the argument. Equivalent means that it compares neither larger nor smaller in the strict weak ordering provided to the std::set.

Therefore, to make your use case work, you want all points in a range to compare equivalent to the range.

If two ranges overlap, then the points shared by the two ranges need to compare equivalent to both ranges. The priority doesn't matter for this, since the equivalence should presumably hold if only one of the ranges is present.

However, one of the defining properties of a strict weak ordering is that the property of comparing equivalent is transitive. Therefore in this ordering the two ranges must then also compare equal in order to satisfy the requirements of std::set.

Therefore, as long as the possible ranges are not completely separated, the only valid strict weak ordering is the one that compares all ranges and points equivalent.

This is however not an order that would give you what you want.

This analysis holds for all standard library associative containers, since they have the same requirements on the ordering.