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digitalmars.D.learn - A tutorial on D templates

reply Philippe Sigaud <philippe.sigaud gmail.com> writes:
[Cross-posted with D.announce, since it's also an annoucement]

Hello all,

I discovered D a few years ago and, seeing the recent increase in community
projects, I
looked for a way to bring my own small part to it.

I quite like D templates and wanted to try LaTeX again, so I decided to bite
the bullet
and wrote a tutorial on templates. It's far from finished and most probably
full of
mistakes but since it's already quite big, I need some inputs.

It's a Github project, here:

https://github.com/PhilippeSigaud/D-templates-tutorial

The resulting pdf is there:

https://github.com/PhilippeSigaud/D-templates-tutorial/blob/master/dtemplates.pdf

(click on View Raw)

If you have any comment, criticism, explanation, what have you, I'm game. What
section
should be expanded, what example would be cool, etc. If you see a mistake, do
not
hesitate to tell me: it's the first time I put thoughts on paper like this.
Github
issues management is far from perfect, but it's usable. Even better would be
pull
requests :)

There is an 'Examples' section where I show what can be done with templates and
there I
'borrowed' some code posted here, with attribution. I already exchanged with
Andrej
Mitrovic (thanks!), but also took some code from Timon Gehr, Simen Kjaeraas,
Trass3r
and Jacob Carlborg. Guys, if any of you have a problem with that, tell me so
and I'll
take down the code of course. But if any of you could give me some explanation
(a small
paragraph or two?) about what your code does, I'll be forever grateful :)

This also extend to anyone who would want to share some template love/lore with
the
rest of us.

Philippe
Jan 13 2012
next sibling parent "Joel" <joelcnz gmail.com> writes:
Good work Philippe, looks good!
Jan 14 2012
prev sibling parent reply =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Fri, 13 Jan 2012 22:21:52 +0100, Philippe Sigaud  
<philippe.sigaud gmail.com> wrote:


 There is an 'Examples' section where I show what can be done with  
 templates and there I
 'borrowed' some code posted here, with attribution. I already exchanged  
 with Andrej
 Mitrovic (thanks!), but also took some code from Timon Gehr, Simen  
 Kjaeraas, Trass3r
 and Jacob Carlborg. Guys, if any of you have a problem with that, tell  
 me so and I'll
 take down the code of course. But if any of you could give me some  
 explanation (a small
 paragraph or two?) about what your code does, I'll be forever grateful :)




The extended enum example does not compile, because you've removed the
unittest{} block around the the tests. I'd say the code in your document
should compile straight out of the box, to be newb-friendly.

As for an explanation:



string EnumDefAsString(T)() if (is(T == enum)) {
     string result = "";
     foreach (e; __traits(allMembers, T))
         result ~= e ~ " = T." ~ e ~ ",";
     return result;
}

This piece of code iterates over all members of the passed enum T,
generating a string containing all members and their values. For
this enum:

   enum bar {
       a, b, c
   }

the generated string looks like this (if you want to check this,
feel free to call EnumDefAsString at run-time and print its result):

   "a = bar.a,b = bar.b,c = bar.c"

As we can see, this is a valid body for an enum. That means we can use
mixin() to generate this exact same enum. But wait - there's more:


template ExtendEnum(T, string s)
     if (is(T == enum) &&
     is(typeof({mixin("enum a{"~s~"}");})))
{
     mixin(
     "enum ExtendEnum {"
     ~ EnumDefAsString!T()
     ~ s
     ~ "}");
}

This code concatenates the string generated from the previous function
with that passed to the function as parameter s. So with bar previously
defined, and this instantiation:

     ExtendEnum!(bar, "d=25")

the body of the function will look like this (after string expansion):



     mixin(
     "enum ExtendEnum {"
     ~ "a = bar.a,b = bar.b,c = bar.c"
     ~ "d=25"
     ~ "}");

concatenating those strings, we see that we have a valid enum definition:

     enum ExtendEnum {a = bar.a,b = bar.b,c = bar.c,d=25}

The mixin then pastes it in, and it is compiled as regular D code.


TLDR:

This code generates an enum definition as a string, by taking all the
members of the old enum, and adding those passed in string parameter s,
and mixing it in.
Jan 16 2012
next sibling parent Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Mon, Jan 16, 2012 at 17:36, Simen Kj=C3=A6r=C3=A5s <simen.kjaras gmail.c=
om> wrote:

 The extended enum example does not compile, because you've removed the
 unittest{} block around the the tests. I'd say the code in your document
 should compile straight out of the box, to be newb-friendly.



Yeah. I just coded a small D script that extract all code samples,
compile them and store the result in a log.
That way, I can now slowly make all samples compile.

I hesitate between showing the boilerplate or not (imports, empty
mains or code in main...)



 As for an explanation:




 This code generates an enum definition as a string, by taking all the
 members of the old enum, and adding those passed in string parameter s,
 and mixing it in.



Thanks! I'll add it.
Jan 16 2012
prev sibling parent =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Tue, 17 Jan 2012 00:10:41 +0100, Philippe Sigaud  =

<philippe.sigaud gmail.com> wrote:


 On Mon, Jan 16, 2012 at 17:36, Simen Kj=C3=A6r=C3=A5s <simen.kjaras gm=





 wrote:

 The extended enum example does not compile, because you've removed th=







 unittest{} block around the the tests. I'd say the code in your docum=







 should compile straight out of the box, to be newb-friendly.



 Yeah. I just coded a small D script that extract all code samples,
 compile them and store the result in a log.
 That way, I can now slowly make all samples compile.

 I hesitate between showing the boilerplate or not (imports, empty
 mains or code in main...)



I would say it should be there. If possible, perhaps have those pieces a=
ll
gray, to mark them as unimportant?
Jan 17 2012