• saotome <saotome.ran googlemail.com> Dec 11 2008
• Lars Ivar Igesund <larsivar igesund.net> Dec 11 2008
• "Jarrett Billingsley" <jarrett.billingsley gmail.com> Dec 11 2008

saotome <saotome.ran googlemail.com> writes:

Hi,

can someone tell me how can i check whether a type is comparable ? Is there
something like "IComparable" in C# ?

Lars Ivar Igesund <larsivar igesund.net> writes:

saotome wrote:

 Hi,
 
 can someone tell me how can i check whether a type is comparable ? Is
 there something like "IComparable" in C# ?


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
something like "IComparable" in C# ?


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
of IComparable<Foo> in C#), you're probably out of luck.  Thankfully,
most of the time you shouldn't be dealing with Object references
anyway.  That's what templates are for :)