Re: How can I tell if the give parameter can be run at compile time?

[H. S. Teoh via Digitalmars-d-learn]

On Mon, Mar 01, 2021 at 08:05:57PM +, 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

-- 
They pretend to pay us, and we pretend to work. -- Russian saying

Re: How can I tell if the give parameter can be run at compile time?

[Adam D. Ruppe via Digitalmars-d-learn]

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.

How can I tell if the give parameter can be run at compile time?

[Jack via Digitalmars-d-learn]

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));