String Mixins

[Travis Boucher]

Bill Baxter wrote:
> On Mon, Nov 16, 2009 at 3:42 PM, Travis Boucher
> <boucher.travis at gmail.com> wrote:
>> I've been playing with string mixins, and they are very powerful.
>>
>> One thing I can't figure out is what exactly can and cannot be evaluated at
>> compile time.
>>
>> For example:
>>
>> ----
>> char[] myFunc1() {
>>        return "int a = 1;";
>> }
>>
>> char[] myFunc2() {
>>        char[] myFunc3() {
>>                return "int b = 2;";
>>        }
>>        return myFunc3();
>> }
>>
>> void main() {
>>        mixin(myFunc1());
>>        mixin(myFunc2());
>> }
>> ----
>>
>> myFunc1() can be used as a string mixin.
>> myFunc2() can't be.
>>
>> I'm sure there are other things that I'll run into, but I figure there is
>> some simple set of rules of what can and can't be used as a string mixin.
> 
> Unfortunately there aren't any easy rules to go by.  If it doesn't
> work CTFE, and a bug hasn't already been filed, then you could file a
> bug, especially if you find the problem blocking your progress.
> However, at this point there are plenty of things that don't work that
> are known and being targeted by Don already.  So a flood of "this and
> that don't work in CTFE" bug reports may not be so useful just yet.
> 
> Anyway, just be thankful that it now at least tells you what can't be
> evaluated.  That's a vast improvement over the old days when the
> compiler would just give a generic error message about CTFE and leave
> you guessing about which line it didn't like!
> 
> --bb

Don responded in D.learn.  The examples above should work on recent 
(>=1.047) DMD, I happen to be using gdc with 1.020.  Right now I am just 
seeing how far I can push it and how weird I can make code that works.