Editing Double dispatch (section)

===A common idiom===
The common idiom, as in the examples presented above, is that the selection of the appropriate algorithm is based on the call's argument types at runtime. The call is therefore subject to all the usual additional performance costs that are associated with dynamic resolution of calls, usually more than in a language supporting only single method dispatch. In [[C++]], for example, a dynamic function call is usually resolved by a ''single'' [[Offset (computer science)|offset]] calculation - which is possible because the compiler knows the location of the function in the object's [[virtual method table|method table]] and so can statically calculate the offset. In a language supporting ''double'' dispatch, this is slightly more costly, because the compiler must generate code to calculate the method's offset in the method table at runtime, thereby increasing the overall [[instruction path length]] (by an amount that is likely to be no more than the total number of calls to the function, which may not be very significant).