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digitalmars.D.learn - Compile Time Argument Evaluation

reply "DProgrammer2" <register102 snet.net> writes:
Hello,

I was wondering if there would be some way to verify arguments to 
a function at compile time, but at runtime call only one function 
(in D2).

To clarify what I mean:

Say you have something like printf()

printf(const char[] format, ...)

I want to be able to make sure the arguments passed into the 
varadic part match what the format string says at compile time. I 
could do this with a template, but then it generates a new 
printf() function for each combination of arguments, and I'm 
trying to avoid that. It might be possible to solve this with a 
mixin as well, but I'd like to avoid writing:

     mixin(SomeFunc!("args", t1, t2, t3))

(Maybe alias would be useful? My D skills aren't that great yet)

I would like it to be more like a regular function call

     SomeFunc("format", t1, t2) // Or something similar

If there's no good way to do this that's fine.

I bring this up because I saw

https://github.com/xomboverlord/xomb/blob/unborn/kernel/core/kprintf.d

which was neat, but it generates a new kprintf function for 
different arguments. I thought it'd be interesting to try and 
have the benefits of compile time checking without the extra 
generated code.

Thank you
Jan 03 2013
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
DProgrammer2:


 If there's no good way to do this that's fine.

 I bring this up because I saw

 https://github.com/xomboverlord/xomb/blob/unborn/kernel/core/kprintf.d

 which was neat, but it generates a new kprintf function for 
 different arguments. I thought it'd be interesting to try and 
 have the benefits of compile time checking without the extra 
 generated code.


I think currently there is no other way. Despite it's something 
I'd like a lot.

Someday I'd like a function like this in Phobos, that verifies 
the formatting string at compile-time:

ctwritefln!"%d %s"(5, "hello");

Such function can be written with just a very light wrapper 
around a normal writefln (and later to something more optimized). 
This means that the actual template bloat can be minimized a lot, 
but not fully removed.

Bye,
bearophile
Jan 03 2013
parent Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Fri, Jan 4, 2013 at 2:59 AM, bearophile <bearophileHUGS lycos.com> wrote:


 Someday I'd like a function like this in Phobos, that verifies the


 formatting string at compile-time:

 ctwritefln!"%d %s"(5, "hello");

 Such function can be written with just a very light wrapper around a
 normal writefln (and later to something more optimized). This means that
 the actual template bloat can be minimized a lot, but not fully removed.


You can find a partial version in a template tutorial I put on github.

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

Select either of the .md, .pdf, .html or .epub version of the tutorial.
It's section 5.11 "Statically-Checked Writeln".

The code worked the last time I launched the automated extractor/tester
(before 2.061).
Jan 04 2013