bool g(T)(T)
{
 	return __traits(compiles, mixin("{ enum a = t; }"));
}


int a;
enum s = "";
// both return false but g(s) is expected to return true
pragma(msg, g(s));
pragma(msg, g(a));

On Monday, 1 March 2021 at 20:05:57 UTC, Jack wrote:
> int a;
> enum s = "";
> // both return false but g(s) is expected to return true

So the value must be known at compile time without any extra context. So that `a` variable might be changed somewhere else so compile time can't read or write it.

`enum` is only allowed to be set once (and at compile time!) so it is allowed at CT too.

`static immutable` generally allows it too since it must be set at declaration then never changed again.

But almost any mutable variable is no go unless it is directly returned from a function which itself can be called at compile time.

On Mon, Mar 01, 2021 at 08:05:57PM +0000, Jack via Digitalmars-d-learn wrote:
> bool g(T)(T)
> {
>  	return __traits(compiles, mixin("{ enum a = t; }"));
> }
> 
> 
> int a;
> enum s = "";
> // both return false but g(s) is expected to return true
> pragma(msg, g(s));
> pragma(msg, g(a));

https://wiki.dlang.org/User:Quickfur/Compile-time_vs._compile-time


T

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