Re: Reprise: 'in out' parameters for functions

["Alexander E. Kopilovich" <aek@VB1162.spb.edu>]

Stephen Leake wrote:

> > > This is what I wanted to declare:
> > >
> > > function Parse
> > >   (Error_Label : in     String;
> > >    Token       : in out Token_List.List_Iterator)
> > >   return String;
> > >   --  Process Token, which should contain '([Config_File =>] <string>)'.
> > >   --  Return the string.
> > >   --  Delete parsed tokens from Token.
> > >
> > One thing is missing in this your explanation: why exactly you don't want to
> > make that List_Iterator global (instead of passing it as IN OUT argument) ?

> My answer is "I never make anything global unless it has to be,
> because that usually leads to trouble".

Yes, but this is general attitude, and it says nothing definite about
particular case - it can be that detailed analysis of this particular case
will show reasons to make it global.

> In this case, Token is actually the contents of an aggregate, part of
> a larger statement that is dynamically allocated. It must be modified
> in place; copying it to a global to pass it to this routine would be a
> maintenance nightmare.

I did not think about copying. I think that real question may be whether
Parse conceptually deals with Token_List.List_Iterator or with the whole
List_Iterator. In the latter case a global is generally possible without any
copying.

> And no, I don't consider "Ada doesn't allow 'in out' in functions" a
> good reason to make something global; I'll change it to a procedure
> first.

Certainly. But there may be other reasons (originated from detailed design).



Alexander Kopilovich                      aek@vib.usr.pu.ru
Saint-Petersburg
Russia