"David Abrahams" <dave@boost-consulting.com> wrote in message news:uk6xhf6kh.fsf@boost-consulting.com...
"Andy Little" <andy@servocomm.freeserve.co.uk> writes:
"David Abrahams" <dave@boost-consulting.com> wrote
"Andy Little" <andy@servocomm.freeserve.co.uk> writes:
"David Abrahams" <dave@boost-consulting.com> wrote
You say you're talking about "operations not types", but I think
hmmm.. Actual quote is " I am talking about operations rather than types after all."
you're just mystifying something that's simple. Whether or not multiplication is commutative depends entirely on the types of its operands.
Whether or not a binary operation is commutative depends on the operator and the types and values of its operands. int x=10,y=x; assert(y/x == x/y);assert(y-x == x-y);
I found output of (say) operator + as "+" useful in following the execution of expression templates. "super-functional" is an off-the-cuff replacement for <functional>. Dont take it too seriously, but std::plus etc are past their best. If I wish to know whether an operation on two types is commutative, I might like to be able to quiz the operation about it. decltype wont do that for me.
And neither should that trait be glommed into the one used for determining result types.
Keep talking... youre winning me over... Though I shall mourn glomming.. for it is a less practised art... [snip]
I need some way to get information about the result types of my value_types operation. eg What results form mux of a interval<double> and a double.
result_of is ok as far as it goes. but 1) There needs to be a common name for Op ie operator_XX or whatever.
Sure.
I suggest operator_plus etc ( cos it's close to operator+)... maybe there are other candidates...?
Otherwise we will all be carrying on our merry own way. That is the status quo.
2) In theory result_of is specializable for functors.
It's a fact.
It would be useful to test to find out how well this works in practise. Results on gcc3.2 have not been encouraging.
Maybe a compiler bug?
...but maybe not in gcc.
3) typeof, decltype etc is not standard C++ as it stands. Its a non-starter.
Not neccessarily. We can build a pretty nice typeof replacement that requires just a little help from users.
Any documentation of this you can point me to ....? I hope "a little help from users " means what it says. regards Andy Little