Implementing the named parameter idiom

C++ supports only positional parameters, which means arguments are passed to a function based on the parameter's position. Other languages also support named parameters--that is, they specify parameter names when making a call and invoking arguments. This is particularly useful with parameters that have default values. A function may have parameters with default values, although they always appear after all the nondefaulted parameters. However, if you want to provide values for only some of the defaulted parameters, there is no way to do it without providing values for the arguments that are positioned before them in the function parameters list. A technique called the named parameter idiom provides a method to emulate named parameters, which we will explore in this recipe.

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