A problem with D contracts

[bearophile]

D contract programming lacks the 'old', but there is another different problem.

Allowing only asserts (and calls to only pure/readonly functions) in precoditions, postconditions and invariants opens the door for future software that perform automatic compile-time verification of contracts.

Putting all kind of D code inside contracts will make them very hard to statically verify.

But simple asserts sometimes are not enough to test more complex things. So other more serious contract systems allow for asserts that contain forall, max, min, sets, and few more simple things, this is an example from a system for Java:

/*@ assert (\forall int i; 0 <= i && i < n; a[i] != null);

Beside keeping the door open to future automatic verification, that short style for conditions helps keep them shorter and less buggy (also because it helps psychological 'chunking'). If code inside contracts is long and complex then it too can contain bugs.

Bye,
bearophile