Compile-Time Only Function

[Mike via Digitalmars-d]

On Friday, 23 June 2017 at 10:46:11 UTC, Moinak Bhattacharyya 
wrote:
> Is there an annotation that declares a function compile-time 
> only? I'm attempting to use a mixin string generating function 
> that uses standard druntime imports, but I'm working in a 
> no-stdlib environment. I never need to use this function at 
> runtime (as is the case, I imagine, with a great many of mixin 
> string generating functions) so is there a way I can omit it?

I don't know of any way to generate a compile-time error if a 
function cannot be evaluated at compile-time.  I think you will 
have to use a manifest constant 
(https://dlang.org/spec/enum.html#manifest_constants) to force 
evaluation at compile time.

// If you're not using druntime, you'll have to define the
// string type as an alias to an immutable char array.
// See 
https://github.com/dlang/druntime/blob/master/src/object.d#L41
alias immutable(char)[] string;

string GenString(string a, string b)
{
     return a ~ ", " ~ b;
}

void main()
{
     // `result` is a manifest constant that contains your
     // compile-time string, do as you wish with it
     enum result = GenString("Hello", "World");
}