[phobos] expand for std.metastrings

[kenji hara]

The points of text vs expand are:
- text is comma separated formatting, expand is inlined formatting.
- text is general formatting function, expand is mostly useful in
compile-time, and specialized D code formatting for code generation.
- editor hilighting issue - my editor does not color q{}, so
generating code are colored with normal syntax hilighting. If I use
text and its formatting, code readability will be wrong. I don't like
it.

> Also, if I
> recall correctly the plan is to get a large portion of both phobos and D
> CTFE compatible, which would eventually eliminate the need for the current
> metastrings.
Almost agreed. I think std.metastrings.toStringNow should be
deprecated, and replaced std.conv.to.
The purpose of std.metastrings I think is that has useful utilities
often specialized for code generation.
Expand is just right.

Kenji

2010/11/3 Robert Jacques <sandford at jhu.edu>:
> On Tue, 02 Nov 2010 14:27:28 -0400, kenji hara <k.hara.pg at gmail.com> wrote:
>
>>> enum code = text(q{ enum msg = "I call you "}, count, q{" times"} );
>>> enum code = text(` enum msg = "I call you `, count, ` times;` );
>>> enum code = ` enum msg = "I call you ` ~ count ~ ` times;`
>>> enum code = q{ enum msg = "I call you "} ~ count ~ q{" times"; }
>>
>> 1st and 4th does not generate intended code string, but generates invalid
>> one.
>> expand! generates 3rd code automatically cooperation with mixin.
>> (2nd is ... the code currently others want to generate for run-time
>> performance?)
>
> Opps. Sorry, I tested 2 & 3, but forgot to test 1 & 2. I also seemed to have
> forgotten a " after times in 2 & 3.
>
> Also, what do you mean by: (2nd is ... the code currently others want to
> generate for run-time performance?)
>
>>> I admit ${n} is slightly better than },n,q{, but it's by no means ugly.
>>> (And
>>> using `` instead of q{} makes it better: `,n,`)
>>
>> The advantage of expand! is that escapes string quotations and
>> concatenates correctly while keeping readability of our meta-code
>> well.
>> (In above 3rd, you escape q{} to `` and interpolate "count" *manually*.)
>
> Yes, manually escaping and concatenating, in all but the trivial cases, is
> really annoying. But my main point was that text is both CTFE-able and lets
> you cleanly do everything expand does naturally. Expand is more complex to
> use, isn't self-documenting (i.e. you have to remember to use a mixin), is
> mostly redundant and increases the radius of comprehension of phobos.
> However, it does allow you to escape a token strings inside a nested string
> in a nice in-lined way. So far, the examples don't seem to provide a strong
> argument for yet another text formater beyond text and Format. Also, if I
> recall correctly the plan is to get a large portion of both phobos and D
> CTFE compatible, which would eventually eliminate the need for the current
> metastrings.
>
>
> _______________________________________________
> phobos mailing list
> phobos at puremagic.com
> http://lists.puremagic.com/mailman/listinfo/phobos
>