[fpc-devel] type pointer to record before record.

[Skybuck Flying]

----- Original Message ----- 
From: "Marco van de Voort" <marcov at stack.nl>
To: "FPC developers' list" <fpc-devel at lists.freepascal.org>
Sent: Friday, 29 April, 2011 10:35 AM
Subject: Re: [fpc-devel] type pointer to record before record.


> In our previous episode, Skybuck Flying said:
>> I would first like to remark about this: "This is very newb unfriendly...
>> newbs might not know this... and will get frustrated by this
>> weird/odd/non-intuitive language construction".
>
> It's in all manuals and books that describe pascal pointers that I know 
> off.

A 13 or 15 year old kid that wants to learn pascal might not be able to 
afford such books.

>
>> Now some question about this:
>>
>> 1. Is there a compiler-related technical reason why it has to be like 
>> this ?
>> If so explain shortly...
>
> Yes, as soon as a type block closes (when whatever  next block starts), 
> the
> compiler knows that the types in the block must be completely defined. If
> not he must deal with the possible incomplete state of identifiers
> throughout the whole compiler, now only in the typeblock.

This seems little to nothing new compared to forward declarations, and 
perhaps call sites which call not yet linked in functions and/or perhaps 
while loops which do not yet know the end of the loop or repeat until 
statements.

>
>> 2. Is there perhaps a technical solution for it so this is no longer
>> required ? If so how much effort would a solution cost ?
>
> It's like Joerg remarks about the modifiers. Things can be done, but lead 
> to
> much larger problems to solve elsewhere. It is not worth it.

Give one example of such a problem ? ;)

> That being said, the example is a more easily solved case. Since that is a
> sequence of typeblocks rather than a alternation of different kind of
> blocks.

These type of problems are not easily solved by noobs who don't know this 
very peculiar thing.

> Trouble is that after 42 years of pascal, cases like this can have been 
> done
> deliberate. IOW to limit forward looking and get errors earlier.

Mhoaw weak argument really, these kinds of coding problems are very common 
when coding and programmers will get used to that.

> Changing this and partitioning the Pascal dialects in the ones that have 
> it,
> and the ones that have not (and most will have not) is idiotic.

You might be surprised but free pascal is already different than Delphi in 
this regard,

I came across one such example in the free pascal compiler code itself.

I had to move certain records, and change certain orders, not a huge problem 
for an experienced Delphi programmer like me ;)

(In case you interested in this difference, checkout my svn source tree 
where I attempted to port free pascal to Delphi, then
search comments for "Skybuck" and perhaps "move" or something, somewhere in 
that source code/comments you'll find it).

>> 3. (Does free pascal still follow these restrictions ? I guess so... )
>
> Yes

Not entirely I would think... somewhere there is a difference with Delphi.

>
>> Final question assuming it's solvable::
>>
>> 4. Do you think it's worth to solve this oddity and make the language 
>> more
>> newb friendly and more intuitive ?
>
> No. Not even the trivial repeated "TYPE" case.
>
> Such changes create more confusion that they solve.

I don't think so, not with modern IDE's... if/when I want to know where a 
pointer type is declared I simply use "Find Declaration".

How could that possibly be confusing, especially when we new to the language 
change/feature know what is happening.

For a newb it probably doesn't matter for him it becomes more easy when 
using the new easified language ! ;) =D

(And again frustrating when he tries to port it to the old language).

>
>> 5. Would it break anything ? (I think not... it would be an
>> extension/relaxation of the language...)
>
> The repeated sequence of TYPE not that much, but people would rely on it,

In what possible way would they rely on it ? This seems very strange to me ! 
;)

> and it might confuse people using multiple compiler and dialects (errors
> suddenly happen on different moments)

I don't think so, if they truely test their code on both compilers they will 
code for the compiler with the most restrictions, the new language feature 
does not present a problem for that.

> As soon as you start with also allowing other blocks, then it becomes a
> massive problem.

Neh, I think you exaggerating it greatly ;)

Unless it's allowed to declare these pointer types in other units which are 
used before the record is declared. Which in itself is kinda interesting 
anyway.

And perhaps even when these pointers are used in all kinds of records before 
the record is declared.

On the other hand this would allow some what more flexibility of data 
structures.

In general I don't have problems with how the things currently work, but 
these type limitations seem very odd, I saw C/other language programmers who 
thought it was impossible to do this in pascal... For them it might have 
been a reason to choose C over Pascal.

Bye,
  Skybuck.