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digitalmars.D.learn - Testing for object property supporting "<" comparison

reply Chris Piker <chris hoopjump.com> writes:
Hi D

I'm working on a bit of code that handles selecting one *.front 
from multiple range-ish objects.  It's a select-or-drop algorithm 
for a data streaming service, the details aren't important.

The algorithm takes a range of something I'll call 
"PriorityRange" objects.  PriorityRange objects are like input 
ranges, but have a few extra members.  The set is:

   .empty     :  Returns bool
   .front     :  Returns something non-void
   .popFront():  Return void

   .priority  :  Returns something comparable via "<" to other
                 .priority values for all input PriortyRanges

   .min       :  Returns something comparable to .max below
                 via "<" for all input PriorityRanges

   .max       :  Returns something comparable to .min above
                 via "<" for all input PriorityRanges

I noticed the isInputRange(R) enum from std/range/primitives.d 
and am wondering how to setup a similar check, call it 
"isPriorityRange(PR)".

My problem is that I don't know how to specify that properties 
must be comparable via "<".  I took a look at the Traits module, 
but there are more things that are comparable then Arithmetic or 
Floating point types.  Also, since the compiler will catch 
objects that don't have these properties, maybe an enum check is 
not worth implementing.

Thanks very much for any advice you might have,
Cheers
May 11 2021
parent reply Paul Backus <snarwin gmail.com> writes:
On Tuesday, 11 May 2021 at 19:42:34 UTC, Chris Piker wrote:

 My problem is that I don't know how to specify that properties 
 must be comparable via "<".  I took a look at the Traits 
 module, but there are more things that are comparable then 
 Arithmetic or Floating point types.  Also, since the compiler 
 will catch objects that don't have these properties, maybe an 
 enum check is not worth implementing.


std.traits.isOrderingComparable

https://phobos.dpldocs.info/std.traits.isOrderingComparable.html
May 11 2021
parent Chris Piker <chris hoopjump.com> writes:
On Wednesday, 12 May 2021 at 00:06:52 UTC, Paul Backus wrote:

 On Tuesday, 11 May 2021 at 19:42:34 UTC, Chris Piker wrote:

 std.traits.isOrderingComparable

 https://phobos.dpldocs.info/std.traits.isOrderingComparable.html


Well I feel sheepish, don't know how I missed that one.  Hey 
thanks for pointing it out.
May 11 2021