cpp/iterator/ranges/distance

@1,2@ Returns the number of hops from to. @3@ Returns the size of as a signed integer.

Return value
@1@ The number of increments needed to go from to. @2@ . @3@ If models, returns ; otherwise.

Complexity
@1@ Linear. @2@ Constant. @3@ If models  or if  is modeled, complexity is constant; otherwise linear.