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digitalmars.D.learn - How can I tell if the give parameter can be run at compile time?

reply Jack <jckj33 gmail.com> writes:
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));
Mar 01
next sibling parent Adam D. Ruppe <destructionator gmail.com> writes:
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.
Mar 01
prev sibling parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
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 -- They pretend to pay us, and we pretend to work. -- Russian saying
Mar 01