[fpc-pascal] Optional param modifier

[Sven Barth]

Am 14.04.2019 um 23:48 schrieb Martin Frb:
> As for "documentation". I disagree with the way it is done in oxygen. 
> But I am not sure I have any good alternative.
> For me a class contract (require/ensure) is part of the interface.
>
> So it would have to be like (and similar for plain procedures, no 
> class) // can be all on one line....
>
> type
>   TFoo= class
>      function DoTheFooThing(Foo1, Foo2: TFoo): Tbar;
>         requires
>            assigned(Foo1) or assigned(Foo2): 'Need at least 1 foo, for 
> the connection';
>         guarantees // better than ensure
>            assigned(result);
>            result.KnowsMyFoo = true: 'Connection exists';  // the 
> =true is redundant
>     procedure DoTheBar;
>   end;
>
> So reading this declaration, you immediately know what is valid. And 
> if custom messages are give, they may tell you way
>
> It is to be noted, that requires and guarantees contain conditions 
> (expressions), not pascal code. So technically it is ok, that they are 
> in the interface and not implementation.
> If I want something in the implementation, I can use normal "assert" 
> (which by the way, have often great documenting value)
The problem is that both "require" and "ensure" can check for fields as 
well (think of a setter for example or something that changes the 
state). Thus you could use a field name that the compiler does not yet 
know. So you would need to order your methods in a order dictated by the 
compiler due to the method's implementation instead of an order of your 
own choosing.

And yes, that would also be a problem with "class invariants", though 
there it's more clear if we say that only identifiers can be used that 
have been declared before as it's the same with properties and their 
setters/getters.

Regards,
Sven