[fpc-pascal] Getting info on a procedure parameter

[Constantine Yannakopoulos]

On Tue, Feb 11, 2014 at 4:52 PM, Marco van de Voort <marcov at stack.nl> wrote:

> In our previous episode, Mark Morgan Lloyd said:
> > If a method a.WriteBuff() is passed another method b.finish() as a
> > parameter, can it access b before calling finish(), or would this
> > require an explicit parameter?
> >
> > If yes, how?
>
> tobject(tmethod(func).data)
>

One word of caution though: Not sure about FPC but in Delphi a caller may
pass a class method instead of an instance method to a method variable. In
this case the correct typecast would be:

T
Class(tmethod(func).data)

and AFAIK there is no safe way to test if the bare pointer TMethod.Data
points to an instance or a class VMT in order to do the correct cast
without AVs. Jedi code library (JCL) has an IsObject() and an IsClass()
function but I have found them not to be fullproof and can raise AVs as
well.

Maybe the OP could consider using interfaces instead of method variables.

--
Constantine.
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