Re: test if the alias of a template is a literal

[TheFlyingFiddle via Digitalmars-d-learn]

On Thursday, 27 October 2016 at 14:45:22 UTC, Gianni Pisetta 
wrote:
On Thursday, 27 October 2016 at 14:34:38 UTC, TheFlyingFiddle 
wrote:
On Thursday, 27 October 2016 at 14:04:23 UTC, Gianni Pisetta 
wrote:
Hi all,
but at the moment isStringLiteral will return true even with 
variables of type string. So i searched for a metod to check 
if an alias is a literal value, but found nothing. Anyone 
have any clue on how can be done?

Thanks,
Gianni Pisetta

Not really understanding your problem. Could you include an 
example use that is problematic?

Yea, sorry I missed that.
A really stupid example would be

string var;

alias Sequence = Optimize!( "The", " ", "value", " ", "of", " 
", "var is ", var );

static assert( is( Sequence == AliasSeq!( "The value of var is 
", var ) ) );

writeln( Sequence );

given that you include the code snippet in the first post.

Thanks, Gianni

I think this fixes the problem:

template isStringLiteral(T...) if (T.length == 1) {
    static if(is( typeof(T[0]) == string ))
    {
        enum bool isStringLiteral = !__traits(compiles, &T[0]);
    }
    else
    {
        enum bool isStringLiteral = false;
    }
}

Literals do not have an address but variables do.

However note that:
string var;
static assert(!is(AliasSeq!(var) == AliasSeq!(var)));

It still works at run-time though:
string var = " hello ";
alias Seq = Optimize!("This", " is", " a", " variable! ", var);
//pragma(msg, Seq) //Fails to compile at var
//static assert(is(Seq == AliasSeq!("This is a variable!", 
var))); //Also fails
writeln(Seq); //Still works