The Role of Implicit Conversions in Erroneous Function Argument Swapping in C++

Abstract

Argument selection defects, in which the programmer has chosen the wrong argument to a function call is a widely investigated problem. The compiler can detect such misuse of arguments based on the argument and parameter type in case of statically typed programming languages. When adjacent parameters have the same type, or they can be converted between one another, the potential error will not be diagnosed. Related research is usually confined to exact type equivalence, often ignoring potential implicit or explicit conversions. However, in current mainstream languages, like C++, built-in conversions between numerics and user-defined conversions may significantly increase the number of mistakes to go unnoticed. We investigated the situation for C and C++ languages where functions are defined with multiple adjacent parameters that allow arguments to pass in the wrong order. When implicit conversions are taken into account, the number of mistake-prone function declarations significantly increases compared to strict type equivalence. We analysed the outcome and categorised the offending parameter types. The empirical results should further encourage the language and library development community to emphasise the importance of strong typing and the restriction of implicit conversion.