• saotome (2/2) Dec 11 2008 Hi,
• Lars Ivar Igesund (7/11) Dec 11 2008 Unfortunately not - the relevant operators are defined in opCmp, so they...
• Jarrett Billingsley (26/28) Dec 11 2008 It's not entirely a replacement, but you can use some static checking

saotome <saotome.ran googlemail.com> writes:

Hi,

can someone tell me how can i check whether a type is comparable ? Is there

Lars Ivar Igesund <larsivar igesund.net> writes:

saotome wrote:

 Hi,
 
 can someone tell me how can i check whether a type is comparable ? Is


Unfortunately not - the relevant operators are defined in opCmp, so they will
always be implemented, even if the implementation may not be sane.

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango

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

On Thu, Dec 11, 2008 at 4:05 PM, saotome <saotome.ran googlemail.com> wrote:
 Hi,

 can someone tell me how can i check whether a type is comparable ? Is there


It's not entirely a replacement, but you can use some static checking
to make sure that comparison between two types makes sense using is()
and typeof():

int cmp3(T, U)(T a, U b)
{
	// is(typeof(a < b)) will only evaluate 'true' if a can be compared to b
	static assert(is(typeof(a < b)), "ack, can't compare types '" ~
		T.stringof ~ "' and '" ~ U.stringof ~ "'");

	if(a < b)
		return -1;
	else if(a > b)
		return 1;
	else
		return 0;
}

void main()
{
	cmp3(3, 4); // fine
	cmp3(3, "hello"); // compilation failure
}

However, if you have two Object references and want to see if they're
comparable to one another (i.e. by seeing if they are both instances

most of the time you shouldn't be dealing with Object references
anyway.  That's what templates are for :)