How to check if an array is a manifest constant?

[Jonathan M Davis]

On 2011-04-04 01:16, simendsjo wrote:
> But there is a difference in how they behave, and I have no way of checking
> this behavior. Consider the following little snippet:
> 
> void f(int[] a) {
>     a[0] = -1;
> }
> 
> void main() {
>     int[] a = [1,2,3];
>     static assert(is(typeof(a) == int[]));
>     f(a);
>     assert(a[0] == -1); // a passed by reference, a[0] changed
> 
>     enum b = [1,2,3];
>     static assert(is(typeof(b) == int[])); // a regular int[] you say?
>     f(b);
>     assert(b[0] == -1); // b passed by value, b[0] unchanged
> }

Okay. I just re-read the appropriate section in TDPL, and it's clear from the 
book that it's definitely intended that a new copy of the enum value be 
created every time that it's used (I was under the impression that that was 
buggy behavior, but apparently that's not true - though the fact that 
accessing any array during CTFE results in a copy of that array _is_ buggy 
behavior and should be fixed by Don before the next release).

Regardless of that, however, enum values shouldn't be used in any place where 
they're going to be altered. So, passing such a value to a function which is 
intended to alter the value that it's passed to is just plain a bug on the 
part of the caller. It shouldn't matter to the function being called.

That being the case, I don't see why you would need to determine whether a 
value that you're dealing with is an enum or not using template constraints or 
static if or whatnot. You should know whether the variable that you're using 
is an enum or not. If it is, don't alter it until you've set it to a variable 
- then you alter the variable.

What use case do you have for wanting to know whether a variable is an enum or 
not?

- Jonathan M Davis