[fpc-pascal] Optional param modifier

[Martin Frb]

On 14/04/2019 00:01, Sven Barth via fpc-pascal wrote:
>
> Well, there is Oxygene's concept of Class Contracts (see
> https://docs.elementscompiler.com/Concepts/ClassContracts/ ), so if
> anything in that direction would be done I'd be inclined towards their
> syntax (and I've played with the idea to implement this in FPC for quite
> some time already).
>
> Though of course it wouldn't necessarily solve the point of knowing
> whether one may pass Nil or not, cause especially in compiled code you
> can't look at the source. So the compiler would need to store the
> conditions in the PPU as well, so that the IDE could present them as
> part of the tooltip even if no source is available...

Well it needs to be in the ppu anyway, because even without source, an 
object can be inherited from.

And the inherited method must fulfil some of the conditions
- It can't accept less than its base (requirements can be looser, but 
not tighter)
- It must fulfil the "ensure"s, or be even stricter. (as that would 
still fulfil them)

Also being in the ppu, would allow compile time errors, when passing 
violating constants.

There are a few things about the oxygen syntax.

1) require is outside the begin..end, but ensure is inside.

2) As the nature of those conditions can be inherited, they are more to 
be thought of as declaration, than implementation.
That would call for them to be in the interface. Though of course that 
messes up the interface....