eiffel: a statement for explicitly executing code when assertions are on

Question

Sometimes the checks and contract constructions need an elaboration which wants to be avoided when assertions removed to improve performances and avoid doing useless things with the "only" work of the compiler. I refer for ex. to job in loops checks or other things. Sometimes having to build a function or having to think how to build it without being executed when assertions are on goes away of the intuitive way of the contract and its sense. I refer particularly to the check structure

Is there a way to do something such as

if checks_are_enabled then
    do check stuff here
end
do_some_normal_job
if checks_are_enabled then
    do other check stuff here
end

Can you give a somewhat realistic example, specifically what isn't working? — U. Windl, May 24 '21 at 16:21

score 2 · Accepted Answer · answered Aug 11 '20 at 10:46

Assertions can be turned on and off on a class-by-class basis, with different levels: preconditions, postconditions, invariants, etc. As a result, it would be tricky and unreliable to report when they are enabled or not (consider, for example, inherited code: the checks might be on in one case and off in another). On a methodological level it would also break the idea that a correct program works the same way regardless of assertion monitoring.

What are workarounds?

If assertions are complex, they can be factored out to dedicated queries and look like
```
check
    is_valid: complex_query
end
```
An alternative is to use debug statements:
```
debug ("check_this", "check_that")
    ... some complex code, including assertions
end
```
where "check_this" and "check_that" are debug keys that can be turned on when compiling for debugging.

There are hacks that could work now, but not in the future:

If a complex state needs to be computed and then checked after some operation, it can be saved in an object passed to some function with complex calculations and used later again:

check
    is_valid_before: valid_pre (state) -- The state is computed by `valid_pre`.
end
code_that_does_the_work
check
    is_valid_after: valid_post (state) -- The state is checked by `valid_post`.
end

Some global flag can be used to keep track about assertion monitoring:

check
    is_monitoring_checks
end

where query is_monitoring_checks has side effects:

is_monitoring_checks: BOOLEAN
        -- Record whether assertion checks are turned on.
    do
        is_check_on := True
        Result := True
    end

Then, subsequent code could be written as asked in the question:

 if is_check_on then
     ... -- Do some complex calculations when assertions are turned on.
 end

eiffel: a statement for explicitly executing code when assertions are on

1 Answers1