Calling Conventions for Binary Operations The functions specified in the "use overload ..." direc­ tive are called with three (in one particular case with four, see "Last Resort") arguments. If the corresponding operation is binary, then the first two arguments are the two arguments of the operation. However, due to general object calling conventions, the first argument should always be an object in the package, so in the situation of "7+$a", the order of the arguments is interchanged. It probably does not matter when implementing the addition method, but whether the arguments are reversed is vital to the subtraction method. The method can query this infor­ mation by examining the third argument, which can take three different values: FALSE the order of arguments is as in the current opera­ tion. TRUE the arguments are reversed. "undef" the current operation is an assignment variant (as in "$a+=7"), but the usual function is called instead. This additional information can be used to generate some optimizations. Compare "Calling Conventions for Mutators".