more enum and pragma troubles

[captaindet]

On 2013-08-19 00:31, JS wrote:

> module main;
>
> import std.stdio, std.conv;
>
> template foo(alias T)
> {
> string foo(string s)
> {
> string x = to!string(T) ~ s ~ "yyyy";
> //pragma(msg, x); // pragma see's x as a run time variable(or rather pragma is executed before x is truly defined)
> return x;
> }

well, i think i understand what is going on in your example. here x is a runtime value because 's' is passed as a function argument (always runtime within this very function). template instantiation (this is when pragmas(msg) is already called) comes first and at this time 's' is unknown, as the instantiated function could be later called with whatever 's' - the compiler cannot know what 's' at this point.

tricks i found around this:

a) if current structure of example program is required (i.s. definition of foo), add a wrapper template for compile time printing:

template _dbg_foo(alias T, string s){
	enum x = foo!(T)(s);
	pragma(msg, x);
	enum _dbg_foo = x;
}

b) if foo does not need to have 's' as an argument, make it a template parameter, too. you also have to use an enum instead of a string for temporary storage:

string foo2(alias T, string s)(){
         enum x = to!string(T) ~ s ~ "yyyy";
         pragma(msg, x);
          return x;
}


the problems i currently face during CTFE are more like:
a) in some cases manifest enums are broken in that they don't contain working compile time copy&paste values. this is currently the case for TypeTuples. i think this will be fixed in the next DMD release.
b) pragma(msg) has not the same behavior as write() when it comes to formating the output of non-string values, it sometimes needs help, e.g. with a to!string() call.