• David Bennett (29/29) Sep 21 2017 Hi Guys,
• David Bennett (19/25) Sep 21 2017 So far the best I've come up with is :
• Meta (4/32) Sep 21 2017 Try __traits(compiles, { enum _ = arg; }). Creating an enum
• David Bennett (7/22) Sep 21 2017 Ahh, warping it in {} seems to change the timing of the
• B4s1L3 (5/8) Sep 22 2017 Yeah , sure and I have such a template in my library:

David Bennett <davidbennett bravevision.com> writes:

Hi Guys,

Is there an easy way to check if the value of string passed to a 
template is available at compile time?

Here is a cut down example of that I'm doing:

```
string[] escapeCTFE(Args...)(){

     static foreach (arg; Args){

             pragma(msg, "Do work on string: ", arg);
         }else{
             pragma(msg, __traits(identifier, arg), " can only be 
read at runtime");
         }
     }

}

void main(){

     string a = "a";
     static string b = "b";
     enum string c = "c";
     immutable string d = "d";
     const string e = "e";

     enum escape_as_much_as_possible = escapeCTFE!(a,b,c,d,e,"f");
}

```

I know for ints I can use __traits(compiles, int[arg]) but I'm 
not sure about strings.

I believe only a and b should be hidden from pragma right?

Thanks,
David.

David Bennett <davidbennett bravevision.com> writes:

On Thursday, 21 September 2017 at 11:42:36 UTC, David Bennett 
wrote:
 [snip]

 ```
 string[] escapeCTFE(Args...)(){

     static foreach (arg; Args){

 [snip]


So far the best I've come up with is :

```

enum isCTstring(alias arg) = (!isAssignable!(typeof(arg)) || 
__traits(compiles, mixin(` "foo" ~ `~__traits(identifier, arg))));

string[] escapeCTFE(Args...)(){

     static foreach (arg; Args){
         static if(isCTstring!(arg)){
             pragma(msg, "Do work on string: ", arg);
         }else{
             pragma(msg, __traits(identifier, arg), " can only be 
read at runtime");
         }
     }
     return new string[32];
}

```

But this seems quite hackish... any better ideas?

Meta <jared771 gmail.com> writes:

On Thursday, 21 September 2017 at 12:30:15 UTC, David Bennett 
wrote:
 On Thursday, 21 September 2017 at 11:42:36 UTC, David Bennett 
 wrote:
 [snip]

 ```
 string[] escapeCTFE(Args...)(){

     static foreach (arg; Args){

 [snip]


 So far the best I've come up with is :

 ```

 enum isCTstring(alias arg) = (!isAssignable!(typeof(arg)) || 
 __traits(compiles, mixin(` "foo" ~ `~__traits(identifier, 
 arg))));

 string[] escapeCTFE(Args...)(){

     static foreach (arg; Args){
         static if(isCTstring!(arg)){
             pragma(msg, "Do work on string: ", arg);
         }else{
             pragma(msg, __traits(identifier, arg), " can only 
 be read at runtime");
         }
     }
     return new string[32];
 }

 ```

 But this seems quite hackish... any better ideas?

Try __traits(compiles, { enum _ = arg; }). Creating an enum 
necessarily requires that its value is available at compile time.

David Bennett <davidbennett bravevision.com> writes:

On Thursday, 21 September 2017 at 13:52:25 UTC, Meta wrote:
 On Thursday, 21 September 2017 at 12:30:15 UTC, David Bennett 
 wrote:
 On Thursday, 21 September 2017 at 11:42:36 UTC, David Bennett 
 wrote:

 enum isCTstring(alias arg) = (!isAssignable!(typeof(arg)) || 
 __traits(compiles, mixin(` "foo" ~ `~__traits(identifier, 
 arg))));

 [snip]

 But this seems quite hackish... any better ideas?

 Try __traits(compiles, { enum _ = arg; }). Creating an enum 
 necessarily requires that its value is available at compile 
 time.

Ahh, warping it in {} seems to change the timing of the 
execution, this is starting to make a lot of sense to me now. 
(also explains why int[arg] works).

Thats much cleaner and I'll use that from now on.

Thanks a lot!
David

B4s1L3 <b2.temp gmx.com> writes:

On Thursday, 21 September 2017 at 11:42:36 UTC, David Bennett 
wrote:
 Hi Guys,

 Is there an easy way to check if the value of string passed to 
 a template is available at compile time?

Yeah , sure and I have such a template in my library: 
https://github.com/BBasile/iz/blob/master/import/iz/types.d#L627

see just above too, the template "isCompileTimeValue"