Re: BinaryPredicate Question
Otis Bricker <obricker@my-dejanews.com> wrote:
But I am a bit surprised that some have said that the version
operator()(const DataItem&,long) is the one that is needed, though I
might have misunderstood the comments. The couple of compilers I had
tried all worked with the operator()(long,const DataItem&). I tried
something else and found that for lower_bound my current compiler does
seem to want (const DI&,long). I can understand this.
If the test was simply std::less<DataItem>, I would have expected the
upper_bound to be calling less::operator()(myvalue,testValue) and the
first point that passed( or the end of range) would be the result. With
lower_bound and less, I would expect it to be testing
not(less::operator()(testValue,myValue)) and terminating the same way.
Of course, I imagine that it could be implemented in other ways. Or I
could just have my head on backwards today.
Thanks again to all for the help thinking about this.
Otis Bricker
Well upper_bound and lower_bound assume a sorted sequence and a weak
ordering, so that the other relops can be emulated with just the code
for less than. [a user specifiec binary predicate, or operator < ()]
That said there is using normal operators
x > y iff y < x
x <= y iff !(y<x)
x >= y iff !(x < y)
x == y iff !(x<y) && !(y<x)
x != y iff x < y && y < x
note some swaps of the arguments. Safer to provide them all so changing
a compiler again does not provide a problem. Further it makes the
predicate more reusable, and easier to maintain/
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