Hey guys,

I'm trying to iterate over an enumeration which contains strings like the this:

enum FileName : string {
file1 = "file1.ext",
file2 = "file2.ext"
}

I already found this article: http://lists.puremagic.com/pipermail/ digitalmars-d/2007-July/021920.html but it's an enum which contains integers instead of strings, thus I can't use min- or max-property.

Any suggestions -> thanks in advance!

Nrgyzer Wrote:

> Hey guys,
> 
> I'm trying to iterate over an enumeration which contains strings like the this:
> 
> enum FileName : string {
> file1 = "file1.ext",
> file2 = "file2.ext"
> }
> 
> I already found this article: http://lists.puremagic.com/pipermail/ digitalmars-d/2007-July/021920.html but it's an enum which contains integers instead of strings, thus I can't use min- or max-property.
> 
> Any suggestions -> thanks in advance!

I'll just be leaving this here, if you need more explanation ask, but maybe you'll understand:

import std.stdio;

enum FileName : string {
file1 = "file1.ext",
file2 = "file2.ext"
}

void main(string args[])
{
    foreach(a; __traits(allMembers, FileName))
        writeln(mixin("FileName." ~ a));
}

== Auszug aus Jesse Phillips (jessekphillips+D@gmail.com)'s Artikel
> Nrgyzer Wrote:
> > Hey guys,
> >
> > I'm trying to iterate over an enumeration which contains strings
like
> > the this:
> >
> > enum FileName : string {
> > file1 = "file1.ext",
> > file2 = "file2.ext"
> > }
> >
> > I already found this article: http://lists.puremagic.com/
pipermail/
> > digitalmars-d/2007-July/021920.html but it's an enum which
contains
> > integers instead of strings, thus I can't use min- or max-
property.
> >
> > Any suggestions -> thanks in advance!
> I'll just be leaving this here, if you need more explanation ask,
but maybe you'll understand:
> import std.stdio;
> enum FileName : string {
> file1 = "file1.ext",
> file2 = "file2.ext"
> }
> void main(string args[])
> {
>     foreach(a; __traits(allMembers, FileName))
>         writeln(mixin("FileName." ~ a));
> }

I've already worked with the mixin-statement, but the __trait is new. As I can see in the documentation, it provides some interesting features.

Your solution works great, thanks!

On 02/10/2011 08:22 PM, Jesse Phillips wrote:
> Nrgyzer Wrote:
>
>> Hey guys,
>>
>> I'm trying to iterate over an enumeration which contains strings like
>> the this:
>>
>> enum FileName : string {
>> file1 = "file1.ext",
>> file2 = "file2.ext"
>> }
>>
>> I already found this article: http://lists.puremagic.com/pipermail/
>> digitalmars-d/2007-July/021920.html but it's an enum which contains
>> integers instead of strings, thus I can't use min- or max-property.
>>
>> Any suggestions ->  thanks in advance!
>
> I'll just be leaving this here, if you need more explanation ask, but maybe you'll understand:
>
> import std.stdio;
>
> enum FileName : string {
> file1 = "file1.ext",
> file2 = "file2.ext"
> }
>
> void main(string args[])
> {
>      foreach(a; __traits(allMembers, FileName))
>          writeln(mixin("FileName." ~ a));
> }

Why the mixin? Is it (just) to have the output string computed at compile-time?

Denis
-- 
_________________
vita es estrany
spir.wikidot.com

spir Wrote:

> On 02/10/2011 08:22 PM, Jesse Phillips wrote:

> > enum FileName : string {
> > file1 = "file1.ext",
> > file2 = "file2.ext"
> > }
> >
> > void main(string args[])
> > {
> >      foreach(a; __traits(allMembers, FileName))
> >          writeln(mixin("FileName." ~ a));
> > }
> 
> Why the mixin? Is it (just) to have the output string computed at compile-time?

The value of 'a' is the enum field name, not its value. The code will ultimately expand to:

void main() {
          writeln(FileName.file1));
          writeln(FileName.file2));
}

Which in turn will may have its enum contents expanded to the string value. The mixin is required because it is a named enum and 'a' is a string, not an alias:

      writeln(FileName.a)

doesn't work and nor does:

    writeln(FileName.mixin(a));

On 02/10/2011 11:32 PM, Jesse Phillips wrote:
>>> enum FileName : string {
>>> >  >  file1 = "file1.ext",
>>> >  >  file2 = "file2.ext"
>>> >  >  }
>>> >  >
>>> >  >  void main(string args[])
>>> >  >  {
>>> >  >        foreach(a; __traits(allMembers, FileName))
>>> >  >            writeln(mixin("FileName." ~ a));
>>> >  >  }
>> >
>> >  Why the mixin? Is it (just) to have the output string computed at compile-time?
> The value of 'a' is the enum field name, not its value.

Oops! missed this point ;-) Thanks for the explanation, Jesse.

This gave me the opportunity to ask about a detail. The following cannot compile because an argument to string mixin must be a (compile-time) constant:

unittest {
    auto i = 1;
    auto s = "i";
    writeln(mixin("i"));	// compiler happy up to here --> "1"
    writeln(mixin(s));		// compiler unhappy --> "Error: argument to mixin
				// must be a string, not (s)"
}

But in your example the symbol a does not look like a constant, instead it the loop variable. Do, how does it work? Or is it that the compiler is able to (1) detect that the collection beeing traversed (__traits(allMembers, FileName)) is a compile-time constant (2) unroll the loop so as to rewrite it first as:
    foreach(a; ["file1", "file2"])
        writeln(mixin("FileName." ~ a));	// ***
and then as:
    writeln(FileName.file1);
    writeln(FileName.file2);

But this doesn't work, neither:
    auto xx=1, yy=2;
    auto as = ["x","y"];
    foreach(a; as)
        writeln(mixin(a ~ a));
And in fact the line *** is laso not accepted.
So, finally, I understand your code, but not how the compiler processes it so as to see it as a mixin with constant argument.

Denis
-- 
_________________
vita es estrany
spir.wikidot.com

I don't have answers to your other questions.

On 02/10/2011 03:25 PM, spir wrote:

> unittest {
> auto i = 1;
> auto s = "i";

It works if you define s as:

    enum s = "i";

> writeln(mixin("i")); // compiler happy up to here --> "1"
> writeln(mixin(s)); // compiler unhappy --> "Error: argument to mixin
> // must be a string, not (s)"

It now works.

Ali

On 02/11/2011 01:02 AM, Ali Çehreli wrote:
> I don't have answers to your other questions.
>
> On 02/10/2011 03:25 PM, spir wrote:
>
>>  unittest {
>>  auto i = 1;
>>  auto s = "i";
>
> It works if you define s as:
>
> enum s = "i";
>
>>  writeln(mixin("i")); // compiler happy up to here --> "1"
>>  writeln(mixin(s)); // compiler unhappy --> "Error: argument to mixin
>>  // must be a string, not (s)"
>
> It now works.
>
> Ali
>
Thank you, Ali.

denis
-- 
_________________
vita es estrany
spir.wikidot.com

spir Wrote:

> But in your example the symbol a does not look like a constant, instead it the loop variable. Do, how does it work?

Magic.

No really, the best I can tell is that the compiler will try to run the foreach loop at compile-time if there is something in the body that must be evaluated at compile time.

The type you are iterating over must be known at compile-time, and just like any such value it is identified by its type and not its contents. So your array literal could in fact be built with a variable, the fact that it is not doesn't matter.

I'm not sure if much thought has gone into compile-time-looping, the best way to enforce it is to get a function to run at compile time. I think the rule of "when the body needs evaluated at compile-time" is what's used, but this also means that when you try to iterate something like __traits or tupleof and don't use a compile-time construct in the body, you don't get an error or the loop executed.

On 02/11/2011 05:27 AM, Jesse Phillips wrote:
> spir Wrote:
>
>> But in your example the symbol a does not look like a constant, instead it the
>> loop variable. Do, how does it work?
>
> Magic.
>
> No really, the best I can tell is that the compiler will try to run the foreach loop at compile-time if there is something in the body that must be evaluated at compile time.
>
> The type you are iterating over must be known at compile-time, and just like any such value it is identified by its type and not its contents. So your array literal could in fact be built with a variable, the fact that it is not doesn't matter.
>
> I'm not sure if much thought has gone into compile-time-looping, the best way to enforce it is to get a function to run at compile time. I think the rule of "when the body needs evaluated at compile-time" is what's used, but this also means that when you try to iterate something like __traits or tupleof and don't use a compile-time construct in the body, you don't get an error or the loop executed.

Oh yes, I see. This explains why my example using plain constants (predefined values, thus known at compile-time) does not run: there is nothing /forcing/ the compiler (such as a ref to a type), thus the compiler does not even try. Even if would be less complicated, probably, than with __traits.

Denis
-- 
_________________
vita es estrany
spir.wikidot.com