🚀 go-pugleaf

In article <408o8u$c0p@hermes.synopsys.com>,
Mike Chapman  <mchapman@synopsys.com> wrote:
>mfinney@inmind.com wrote:
[ snip snip ]

>>This is why the definitions are wrong.
>>
>
>I disagree. If a and b are not ordered (ie not comparable), it is an
>error to try to compare them. Hence a < b (or any of the other 5 operators)
>are free to do whatever they like - throw an exception, return a random
>value or start up a game of tetris.

	This is an unacceptably severe overconstraint.
I see nothing wrong with a mathematical SET class with < meaning
subset. This relation is a partial order, but "subset" is well defined
for ALL pairs sets.

	The fact is that < is mathematically well defined on 
pointers because they are naturally partially ordered -- but the
ISO C Standard does not require correct computation of this
function for no-comparable operands, and neither does STL.

	The STL definitions were in fact quite wrong and
completely unnacceptable until overloading of function templates by
partial specialisation was introduced into the C++ language.

	Now the definitions in STL remain wrong, but they are
only defaults which can be overriden.

	I personally do NOT like this arrangement (and have
deleted the templates from my copy of STL). I'd prefer a mechanism like:

	class X : total_order ....
	class Y : partial_order

with the default being to issue a diagnostic for an undefined function.
A default, however, is tolerable.

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