Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Graeme Geldenhuys]

On 2016-06-22 18:18, Dennis Poon wrote:
> can we do it in descending order without a user defined enumerator?

Not as far as I know - I believe it is a one directional iterator (or so
the interface suggests). There are tons of limitations with the for..in
construct.

Years back I implemented an iterator interface (based on Java definition
of iterators) with multiple implementations for various container
classes I use often. I can iterate forward, backwards, use a regex to
filter (skip) what gets iterated etc. And using the factory method I can
request an iterator instance with ease, and even register more iterators
if needed. So much more flexible [personal opinion].

I've written an article about it some years back:
  http://geldenhuys.co.uk/articles/

Look for the “Iterator Pattern” article and sample code.

Regards,
  Graeme

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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Dennis Poon]

I saw your document on for x in ListX  loop and would like to reconfirm 
that it is always iterated in ascending order, right?


can we do it in descending order without a user defined enumerator? i.e. 
for simple enumerated type, is there a construct to iterate through it 
in descending order?


Dennis
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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Jürgen Hestermann]

Am 2016-06-21 um 17:16 schrieb Sven Barth:
> It was decided some time ago when mode Delphi was switched to H+ (due to 
Delphi compatibility) that mode ObjFPC won't be switched, cause for that mode we 
value backwards compatibility higher than the user not having to write a switch.

This is quite short-sighted:

It's not only the work of writing a compiler switch.
You also have to *know* (think) about it.
There are so many compiler switches and if we end up
with the situation that all new users have to spend a
day to make their program work as the grandious feature
list of some FPC page told them then something is wrong.

Those who are already familiar with all the details have
much less work to just add a compiler switch to their
existing projects (if needed) and it would be necessary
only once on a certain FPC version when this default
changes.

Now we need to tell each new user that he has to change
the (default) settings to get a "modern" Pascal compiler
because "out of the box" it is a very old one.

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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Sven Barth]

Am 21.06.2016 15:21 schrieb "Michalis Kamburelis" :
>
> 2016-06-21 15:03 GMT+02:00 Sven Barth :
> > Am 21.06.2016 12:31 schrieb "Michalis Kamburelis"
> > :
> >> Current FPC defaults:
> >>
> >> - Help people who except the {$mode fpc} to be default (so they write
> >> code without classes and a lot of other new features),
> >> - Or people who expect that string is by default ShortString (limited
> >> to 255 chars).
> >
> > One might argue about changing the default mode, but changing the
default
> > String type of mode ObjFPC will very likely result in compilation or
runtime
> > errors (probably even in the compiler itself) which is something we
tend to
> > avoid without good reasons. At the very least there will be performance
> > differences which - depending on the code - might be noticeable as well.
> >
>
> These errors and differences will be only felt by projects that use
> {$mode objfpc} but assume that string = ShortString (and they don't
> use {$H-} explicitly). I don't think it would apply to too many
> projects?

Compiler and RTL are two examples.

> And if we do it in some major version, with proper release notes, like
> Mr Bee proposes, these projects would have plenty of time to adjust
> their compilation scripts / config files. They could just add "-Sh-"
> or "{$H-}" and be OK, for both past and future FPC versions.

It was decided some time ago when mode Delphi was switched to H+ (due to
Delphi compatibility) that mode ObjFPC won't be switched, cause for that
mode we value backwards compatibility higher than the user not having to
write a switch.

Regards,
Sven
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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Michalis Kamburelis]

2016-06-21 15:03 GMT+02:00 Sven Barth :
> Am 21.06.2016 12:31 schrieb "Michalis Kamburelis"
> :
>> Current FPC defaults:
>>
>> - Help people who except the {$mode fpc} to be default (so they write
>> code without classes and a lot of other new features),
>> - Or people who expect that string is by default ShortString (limited
>> to 255 chars).
>
> One might argue about changing the default mode, but changing the default
> String type of mode ObjFPC will very likely result in compilation or runtime
> errors (probably even in the compiler itself) which is something we tend to
> avoid without good reasons. At the very least there will be performance
> differences which - depending on the code - might be noticeable as well.
>

These errors and differences will be only felt by projects that use
{$mode objfpc} but assume that string = ShortString (and they don't
use {$H-} explicitly). I don't think it would apply to too many
projects?

And if we do it in some major version, with proper release notes, like
Mr Bee proposes, these projects would have plenty of time to adjust
their compilation scripts / config files. They could just add "-Sh-"
or "{$H-}" and be OK, for both past and future FPC versions.

Regards,
Michalis
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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Sven Barth]

Am 21.06.2016 12:31 schrieb "Michalis Kamburelis" :
> Current FPC defaults:
>
> - Help people who except the {$mode fpc} to be default (so they write
> code without classes and a lot of other new features),
> - Or people who expect that string is by default ShortString (limited
> to 255 chars).

One might argue about changing the default mode, but changing the default
String type of mode ObjFPC will very likely result in compilation or
runtime errors (probably even in the compiler itself) which is something we
tend to avoid without good reasons. At the very least there will be
performance differences which - depending on the code - might be noticeable
as well.

Regards,
Sven
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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Michalis Kamburelis]

>> I even expect a bit further. These {$MODE OBJFPC}, {$H+}, and {$J-}
>> directives should be the *default* directives for every new FPC
>> programs/units. We're now using Free Pascal compiler on 2016. Why do we need
>> to explicitly declare Free Pascal mode in a Free Pascal program? In 21st
>> century, our string should not be limited to 255 chars anymore. And what the
>> hell is "writable constant"? It's contradictio in terminis. :)
>
> We have a strong focus on backwards compatibility, so the default mode stays
> "fpc" and changing a modes' default settings would also affect backwards
> compatibility.
>

Maintaining compatibility is usually a compromise. I feel that in this
case, maintaining such compatibility hurts more than it helps. It is
of course my opinion, biased by the kind of code I write, and by the
programmers I talk with (many of whom don't know Pascal, but know
Java, C# or other OOP languages).

Current FPC defaults:

- Help people who except the {$mode fpc} to be default (so they write
code without classes and a lot of other new features),
- Or people who expect that string is by default ShortString (limited
to 255 chars).

I think that the majority of people use now suitable command-line
options, or directives, to change FPC mode to something more modern
({$mode objfpc} or {$mode delphi}, and {$H+}). So changing the
defaults will not hurt them. Sure, I don't have any hard data to back
it up, I don't know how much is "majority". But this applies at least
to all Lazarus users that have these settings "by default".

Again, this is just my opinion, but I would say that breaking
compatibility in this case is warranted. Making objfpc the default
mode, and making $H+ the default in objfpc mode, before the fpc.cfg is
read (so it applies to everyone, and can be overridden by fpc.cfg or
command-line later) would be a nice thing.

(Making {$J-} would be a cool bonus, but I don't dream about it, as it
could admittedly break more recent code.)

In 
http://michalis.ii.uni.wroc.pl/~michalis/modern_pascal_introduction/modern_pascal_introduction.html
I decided to just write

  {$mode objfpc}{$H+}{$J-} // Just use this line in all modern sources

at the beginning of a first "hello world" example. And I never explain
the reason for this line, I just repeat it in all examples (that are
full programs/units). That's an ugly solution, but I just couldn't see
a better one. It doesn't sound nice to explain that:

- otherwise, they don't have classes ("why are classes disabled?"),
- otherwise their stings are limited to 255 ("are you sure this is a
modern language?"),
- and otherwise their constants are not necessarily constant ("what?") ...

It's not a good learning experience, if you have to learn about so
many historical things when you learn to write a first Pascal program.
And these things are already fixed -- just the defaults are old.

Regards,
Michalis
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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Karoly Balogh (Charlie/SGR)]

Hi,

On Tue, 21 Jun 2016, Mr Bee wrote:

> > Maybe a little bit offtopic, but I have a question regarding the
> >compiler directives: is there a way to tell Lazarus to use these
> >directives in every new unit?

No clue about Lazarus, but one can put -mOBJFPC in his compiler config
file (same with other modes), and tell Lazarus somehow to use that config
file. I'm positive that it's possible and that changes the default. Same
with a lot of other modeswitches or default-changers, if you don't wanna
pollute all your sources with such switches, put it in your config file.
Just don't forget to document these options for your project's build
system.

(And if you use components which expects other modes (Delphi is pretty
common), you might need to add the modeswitch to them instead...)

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Re: [fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Sven Barth]

Am 21.06.2016 08:58 schrieb "Mr Bee" :
>
> > Maybe a little bit offtopic, but I have a question regarding the
compiler directives: is there a way to tell Lazarus to use these directives
in every new unit?
>
> I even expect a bit further. These {$MODE OBJFPC}, {$H+}, and {$J-}
directives should be the *default* directives for every new FPC
programs/units. We're now using Free Pascal compiler on 2016. Why do we
need to explicitly declare Free Pascal mode in a Free Pascal program? In
21st century, our string should not be limited to 255 chars anymore. And
what the hell is "writable constant"? It's contradictio in terminis. :)

We have a strong focus on backwards compatibility, so the default mode
stays "fpc" and changing a modes' default settings would also affect
backwards compatibility.

Regards,
Sven
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[fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Mr Bee]

> Maybe a little bit offtopic, but I have a question regarding the compiler 
>directives: is there a way to tell Lazarus to use these directives in every 
>new unit? I even expect a bit further. These {$MODE OBJFPC}, {$H+}, and {$J-} 
>directives should be the *default* directives for every new FPC 
>programs/units. We're now using Free Pascal compiler on 2016. Why do we need 
>to explicitly declare Free Pascal mode in a Free Pascal program? In 21st 
>century, our string should not be limited to 255 chars anymore. And what the 
>hell is "writable constant"? It's contradictio in terminis. :)
If somehow someone want to deals with those things, let them use the 
appropriate directives explicitly. But for most programs we build today, those 
things should be the default.

–Mr Bee
 

Pada Selasa, 21 Juni 2016 13:15, Marc Hanisch  
menulis:
 

 Thanks Michalis for your excellent work! It's very important to left the early 
90s associated with Pascal programming behind us and to encourage new 
developers to have a look onto the modern aspects of Object Pascal!
Maybe a little bit offtopic, but I have a question regarding the compiler 
directives: is there a way to tell Lazarus to use these directives in every new 
unit?
Best regards,Marc
2016-06-21 7:47 GMT+02:00 Michalis Kamburelis :

2016-06-20 5:31 GMT+02:00 Mr Bee :
[...]
> I have a little suggestion though. I prefer to use {$J-} directive in my
> Pascal program. I think it encourages good programming practice in Pascal.
> The {$J-} means constant is a constant no matter how you declare it. To bad
> FPC is still using {$J+} as the default even in the {$MODE OBJFPC}, which
> means a constant becomes a variable once you include the data type
> eventhough it's declared within a 'const' block. CMIIW.
>

Ouch. For some reason, I thought that {$J-} is the default in {$mode
objfpc} since years, and we have left that mistake behind us. Quick
test showed me that I was mistaken. This makes a *lot* of my code less
safe that I assumed, as in many recent projects I didn't bother to
explicitly use {$J-}.

This is an excellent suggestion then, thank you. I updated the
document to encourage everywhere doing

  {$mode objfpc}{$H+}{$J-}

at the beginning.

I definitely *do not want* to explain to any new programmer what a
"writeable constant" is... This concept should remain buried:)

Regards,
Michalis
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[fpc-pascal] Bls: Bls: Quick Modern Object Pascal Introduction, for Programmers

[Mr Bee]

> I definitely *do not want* to explain to any new programmer what a "writeable 
>constant" is... This concept should remain buried :) Exactly! I also don't 
>understand why the {$MODE OBJFPC} uses the {$J+} as the default. :)

–Mr Bee
 

Pada Selasa, 21 Juni 2016 12:47, Michalis Kamburelis 
 menulis:
 

 2016-06-20 5:31 GMT+02:00 Mr Bee :
[...]
> I have a little suggestion though. I prefer to use {$J-} directive in my
> Pascal program. I think it encourages good programming practice in Pascal.
> The {$J-} means constant is a constant no matter how you declare it. To bad
> FPC is still using {$J+} as the default even in the {$MODE OBJFPC}, which
> means a constant becomes a variable once you include the data type
> eventhough it's declared within a 'const' block. CMIIW.
>

Ouch. For some reason, I thought that {$J-} is the default in {$mode
objfpc} since years, and we have left that mistake behind us. Quick
test showed me that I was mistaken. This makes a *lot* of my code less
safe that I assumed, as in many recent projects I didn't bother to
explicitly use {$J-}.

This is an excellent suggestion then, thank you. I updated the
document to encourage everywhere doing

  {$mode objfpc}{$H+}{$J-}

at the beginning.

I definitely *do not want* to explain to any new programmer what a
"writeable constant" is... This concept should remain buried:)

Regards,
Michalis


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