Al Gonzalez's "WITH" proposal
lazarus / 64-FPC development

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Ñuño_Martínez · 2016-09-19 10:14

Mexican Delphi specialist Al Gonzalez has made a proposal to upgrade
the WITH keyword that I think it's worth to be discussed.  We are
discussing it at the Club Delphi forums.

As you know, WITH keyword seems to be doomed as it's tagged as
dangerous.  The proposal is something like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   WITH
TForm2.Create (NIL) DO    TRY      AppLogger.LogForm (WITH);     
WITH.ShowModal    FINALLY      WITH.Free    END No more than one
object/record per WITH block.No nested WITH blocks allowed.Mandatory
WITH keyword or other symbol to indicate the referenced
object.Original post.

Somebody noted something similar in Python:
Code: PHP  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i with
open('file.txt', 'r') as f:       f.read()       d.write(...)Other
proposals (in the same thread at Club Delphi) are:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   WITH
TForm2.Create (NIL) DO    TRY      &ShowModal    FINALLY      &Free  
END 
and
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   WITH
TForm2.Create (NIL) DO    TRY      .ShowModal    FINALLY      .Free  
END 
There's also a proposal to declare an alias:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   WITH Obj:
TForm2.Create (NIL) DO    TRY      Obj.ShowModal    FINALLY     
Obj.Free    END 
Or use a default naming like SELF or RESULT.  The proposal is "IT".

My opinion is mixed.  I don't like WITH.  Years ago I used it a lot in
a big project and now it's hard to read that code, so now I used it a
few times, mostly in small code snipets like:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i (*
Initializes state. *)  PROCEDURE TGeckoMovement.Enter;  BEGIN    WITH
TgoiGecko (StateMachine.Owner) DO    BEGIN      InicitAnimation
(FP_WALK, FP_WALK + NUM_FP_CALK, V_ANIMATION);      Flipped := (Random
(2) = 1)    END  END; 
But sometimes I use something like:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i (*
Initializes state. *)  PROCEDURE TGeckoMovement.Enter;  VAR    Gecko:
TgoiGecko;  BEGIN    Gecko := TgoiGecko (StateMachine.Owner);   
Gecko.InicitAnimation (FP_WALK, FP_WALK + NUM_FP_CALK, V_ANIMATION); 
 Gecko.Flipped := (Random (2) = 1)  END; I think that a redefinition
would be useful.

What do you think?

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marcov · 2016-09-19 10:23

I don't like it since it breaks the predeclaration of variables of
Pascal.

Maybe Python allows inline declaration of variables, but Pascal
definitely not.

I also think the problem is not big enough to actually warrant extra
syntax.  IMHO it is only needlessly expanding the language as a hobby
language designer.

The big problems are not in language syntax, but in (multiplatform)
libraries and maintenance

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rvk · 2016-09-19 11:11

Quote from: Ñuño_Martínez on September 19, 2016, 12:14:06 pmAs you
know, WITH keyword seems to be doomed as it's tagged as dangerous. 
The proposal is something like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i with
TForm2.Create(nil) dotry  AppLogger.LogForm(with); 
with.ShowModalfinally  with.Freeend;What would be the advantage over
this?
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var  f:
TForm2;begin  f := TForm2.Create(nil);  try    AppLogger.LogForm(f); 
 f.ShowModal  finally    f.Free  end;In both cases you can use short
variable-names. Only in Pascal you would need to declare the variable
(which, like marcov also mentioned, would always be needed). Even for
the "for x in y", the x needs to be declared.

The only possible form I would see is with the "as"-keyword.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i with
TForm2.Create(nil) as myform dotry  AppLogger.LogForm(myform); 
myform.ShowModalfinally  myform.Freeend;This would be similar as
casting with "as" but with creating a variable on the fly.

(But again... that's not how Pascal works)

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mse · 2016-09-19 11:35

Quote from: rvk on September 19, 2016, 01:11:22 pmThis would be
similar as casting with "as" but with creating a variable on the fly.

(But again... that's not how Pascal works)
Actually Pascal "with" statement creates a pointer variable on the
fly, what is missing that it gets a name. There is a very old Pascal
dialect which supports such a safe with statement, I don't remember
the name, you'll find it in FPC mailing list archive. It has been
discussed many times.
I long gave up to hope that Free Pascal will support it too, unless it
becomes "Delphi compatible".

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Michaela Joy · 2016-09-26 22:39

Personally, I wouldn't use it. I'm not keen about using the with
statement as it is. There are too many instances where it makes the
code appear to be unclear.
(i.e. properties / methods appear to clash)

But that's me. Others may and probably will see it differently.

@rvk: I agree with you. I see your example as being clearer and easier
to read and understand.

Just my opinion. FWIW.

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Remy Lebeau · 2016-09-29 01:59

Quote from: rvk on September 19, 2016, 01:11:22 pmThe only possible
form I would see is with the "as"-keyword.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i with
TForm2.Create(nil) as myform dotry  AppLogger.LogForm(myform); 
myform.ShowModalfinally  myform.Freeend;
Except the code would be ambiguous if a real type-cast is needed and
the 'with' operates on the result of the cast.  If you are going to
introduce aliasing, a new syntax would be needed that is not
ambiguous.

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skalogryz · 2016-09-29 02:16

Quote from: marcov on September 19, 2016, 12:23:14 pmI don't like it
since it breaks the predeclaration of variables of Pascal.
the only exception is made for exceptions

Code: [Select]try
 ..
except
  on e: exception do ...
end;
(need to be noted, this is not quite an exception to predeclaration
rule, since the exception variable is predeclared ahead of the
handling code. But it definitely looks like inline declaration,
similar to C-ish Code: [Select]for (var i=0...) 
)

On topic: these days IDEs have all sorts of features for mass-code
generation/editing, that it makes with-statement irrelevant (no matter
if syntax is changed or not)