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(C++) function design

Function design is the correct design of a function. Exercise #2: correct function declarations is an exercise in correct function design.

The most important to get correct is the function declaration.

Here are some rules:

The name of the function should say what it does

• Do use names like Swap, GetDistance, StrToInt
• Do not use names like DoIt, Transmogrify, Stuff
• Exceptions: Transmogrify is a function name commonly used in the literature to denote a function you are not aware of what it is doing

Make a function responsible for one thing

• Do not use names with 'And' in it, like SwapAndGetMean
• Do use two functions instead, Swap and GetMean
• Exceptions: some mathematical functions can cooperate and so improve runtime speed: MeanAndStdDev executes faster then calling the seperate functions for Mean and StdDev

The return type is expected from the name of the function

• Do give a function a void return type when it has no return type
• Do return a non-pointer non-reference object when a function is expected to always execute successfully on the assumptions that its arguments are valid
• Do return a pointer (or better: a smart pointer) to a data type when the return type can be null, that is: empty. If the pointer needs to be read-only, make it const (for example 'const T * const GetT()', where GetT is a function that returns a pointer to a T)
• Do not make a function return a reference to a function's local variable, this leads to undefined behavior
• Do not make a function return an error code, use exceptions instead

The function arguments are expected from the name of the function

• Do use a pointer (or better: a smart pointer) to a data type when the argument can be null, that is: empty. If the pointer needs to be read-only, make it const (for example 'void CoutT(const T * const t)', where CoutT is a function that uses std::cout on a T)
• Do use a non-pointer reference object for expensive-to-copy data types, like std::string, std::vector<int> or Database. Make the argument const if it must be marked read-only
• Do use a non-pointer non-reference object for standard data types like int. Make the argument const if it must be marked read-only

The function must specify the called what input it can't handle

• Do use assert and exceptions to make clear to the client which input the function cannot handle. For example, the square root of a negative number does not exist
• Do not use error codes as return types

References

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