• Trass3r <mrmocool gmx.de> Jun 04 2009
• Jarrett Billingsley <jarrett.billingsley gmail.com> Jun 04 2009
• Trass3r <mrmocool gmx.de> Jun 04 2009
• Robert Clipsham <robert octarineparrot.com> Jun 05 2009

Trass3r <mrmocool gmx.de> writes:

I tried to use a function lookup table to quickly access a particular one.
But the compiler (dmd1) complains about
Error: non-constant expression & func

I guess because it's used inside a class since &func is of type 
function, not delegate?


Here's a stripped down example:

protected Object function(int)[] lookup = [
	&func
];

protected Object func(int)
{
	return null;
}

Jarrett Billingsley <jarrett.billingsley gmail.com> writes:

On Thu, Jun 4, 2009 at 12:42 PM, Trass3r <mrmocool gmx.de> wrote:
 I tried to use a function lookup table to quickly access a particular one.
 But the compiler (dmd1) complains about
 Error: non-constant expression & func

 I guess because it's used inside a class since &func is of type function,
 not delegate?


You've got it the other way around.  If func is an instance method
(non-static method) of a class, &func is a delegate, not a function.

It can't evaluate &func at compile-time because there is no way to
create a delegate at compile-time.  You need an instance to create a
delegate, which you can only create by using 'new', which only works
at runtime.

Trass3r <mrmocool gmx.de> writes:

Jarrett Billingsley schrieb:
 On Thu, Jun 4, 2009 at 12:42 PM, Trass3r <mrmocool gmx.de> wrote:
 I tried to use a function lookup table to quickly access a particular one.
 But the compiler (dmd1) complains about
 Error: non-constant expression & func

 I guess because it's used inside a class since &func is of type function,
 not delegate?


 You've got it the other way around.  If func is an instance method
 (non-static method) of a class, &func is a delegate, not a function.
 


I know, but if I change that array to delegates, dmd complains:
Error: cannot implicitly convert expression (&func) of type Object 
function(int) to Object delegate(int)


 It can't evaluate &func at compile-time because there is no way to
 create a delegate at compile-time.


Yeah, gotta use a different approach.

Robert Clipsham <robert octarineparrot.com> writes:

Jarrett Billingsley wrote
 It can't evaluate &func at compile-time because there is no way to
 create a delegate at compile-time.


I believe that LDC used to support this, but had to remove the 
functionality due to some bugs with it/to be compatible with dmd.