State preconditions (if any)

Reason

Arguments have meaning that might constrain their proper use in the callee.

Example

Consider:

double sqrt(double x);

Here x must be non-negative. The type system cannot (easily and naturally) express that, so we must use other means. For example:

double sqrt(double x); // x must be non-negative

Some preconditions can be expressed as assertions. For example:

double sqrt(double x) { Expects(x >= 0); /* ... */ }

Ideally, that Expects(x >= 0) should be part of the interface of sqrt() but that's not easily done. For now, we place it in the definition (function body).

References: Expects() is described in GSL.

Note

Prefer a formal specification of requirements, such as Expects(p);. If that is infeasible, use English text in comments, such as // the sequence [p:q) is ordered using <.

Note

Most member functions have as a precondition that some class invariant holds. That invariant is established by a constructor and must be reestablished upon exit by every member function called from outside the class. We don't need to mention it for each member function.

Enforcement

(Not enforceable)

See also: The rules for passing pointers. ???