Don't insist on having only a single `return`-statement in a function

Reason

The single-return rule can lead to unnecessarily convoluted code and the introduction of extra state variables. In particular, the single-return rule makes it harder to concentrate error checking at the top of a function.

Example

template<class T>
//  requires Number<T>
string sign(T x)
{
    if (x < 0)
        return "negative";
    if (x > 0)
        return "positive";
    return "zero";
}

to use a single return only we would have to do something like

template<class T>
//  requires Number<T>
string sign(T x)        // bad
{
    string res;
    if (x < 0)
        res = "negative";
    else if (x > 0)
        res = "positive";
    else
        res = "zero";
    return res;
}

This is both longer and likely to be less efficient. The larger and more complicated the function is, the more painful the workarounds get. Of course many simple functions will naturally have just one return because of their simpler inherent logic.

Example

int index(const char* p)
{
    if (!p) return -1;  // error indicator: alternatively "throw nullptr_error{}"
    // ... do a lookup to find the index for p
    return i;
}

If we applied the rule, we'd get something like

int index2(const char* p)
{
    int i;
    if (!p)
        i = -1;  // error indicator
    else {
        // ... do a lookup to find the index for p
    }
    return i;
}

Note that we (deliberately) violated the rule against uninitialized variables because this style commonly leads to that. Also, this style is a temptation to use the goto exit non-rule.

Alternative

• Keep functions short and simple
• Feel free to use multiple return statements (and to throw exceptions).