bugprone-standalone-empty

Warns when empty() is used on a range and the result is ignored. Suggests clear() if it is an existing member function.

The empty() method on several common ranges returns a Boolean indicating whether or not the range is empty, but is often mistakenly interpreted as a way to clear the contents of a range. Some ranges offer a clear() method for this purpose. This check warns when a call to empty returns a result that is ignored, and suggests replacing it with a call to clear() if it is available as a member function of the range.

For example, the following code could be used to indicate whether a range is empty or not, but the result is ignored:

std::vector<int> v;
...
v.empty();

A call to clear() would appropriately clear the contents of the range:

std::vector<int> v;
...
v.clear();

Limitations:

• Doesn’t warn if empty() is defined and used with the ignore result in the class template definition (for example in the library implementation). These error cases can be caught with [[nodiscard]] attribute.