What the heck is wrong with CTFE's?

[JS]

On Monday, 8 July 2013 at 12:11:36 UTC, Dicebot wrote:
> On Monday, 8 July 2013 at 12:08:44 UTC, JS wrote:
>> the issue with the foreach is still under question though, 
>> when I try to use a for loop with i and access TT[i] I get an 
>> error about i not being compile time readable. (maybe this is 
>> because of how the type tuple is defined? possibly need a 
>> index method to get the value?)
>
> Because i is not a compile-time value, it is a normal variable. 
> And TT is a type tuple, pure compile-time entity. You really 
> need to study the documentation on this topic or frustration 
> will continue.

This has nothing to do with it...

string name = "Value"~((i==0) ? "" : (to!string(i)));
i++;

works, but

string name = "Value"~((i==0) ? "" : (to!string(i++)));

but doesn't....


It is a matter of placement of the increment operation on i that 
is breaking the code and has nothing to do with your default 
answer of "you don't know how CTFE's work, read the docs!" and 
"... it's not a compile-time variable".

If i's not possible to use at compile time then none of the 
following code examples should work

One could argue that depending on how to!string works could be 
the issue, but this has nothing to do with i, which is what you 
have stated, but to!string.

If it is to!string or templates in general that are the issue 
then it is confusing to have the same syntax for compile time and 
runtime but some common runtime syntax doesn't work.

e.g.,

	int x = 0;
	writeln(x);
	to!string(x++);
	writeln(x);

works fine at run-time, but to!string(i++) fails and 
to!string(i); i++; works in CTFE...

So, either this is what you were getting at but didn't explain it 
well(making the issue about i when it is about CTFE templates) or 
you didn't understand the issue yourself.


	int i = 0;
	foreach(t; T)
	{
		string name = "Value"~((i==0) ? "" : (to!string(i)));
		i++;
	}



vs

	int i = 0;
	foreach(t; T)
	{
		string name = "Value"~((i==0) ? "" : (to!string(i++)));		
	}

vs


	foreach(i, t; T)
	{
		string name = "Value"~((i==0) ? "" : (to!string(i)));
	}


all are suppose to do the same thing and are all essentially 
semantically identical... they should do the same. (at least 
according to your logic and the compiler error message that says 
the issue is with i)