Operator overloading advise

[jacob navia]

Hi
I am implementing operator overloading in the context of
the C language.

I would like to have your opinion about this:

Would it be a good idea to assume that the
operator != could be synthethized from

! a == b (operator_equal)

operator >= could be built from ! operator<
operator < could be built from ! operator>=

etc etc.

This would greatly reduce the number of operator
functions that the user needs to implement...

In the same style a == b implies that b == a isn't it?
This means that

int operator==(foo &a,int &b) is the same as
int operator==(int &b,foo &a)

making == and != commutative.

Another step would be to assume commutativity
in the arithmetic operators, what is kind of riskier.

A+B != B+A if you overload the "+" for strings:

"1234" + "5678" --> "12345678", but
"5678" + "1234" --> "56781234"

What guidelines should be sensible to follow?

Thanks in advance for your comments

jacob

[Kyle]

> What guidelines should be sensible to follow?

That heavily depends on the thing ur trying to model (although i cant
imagine right now types where a==b doesnt imply ! a!=b [im not that
imaginative though]).

As for the guidelines ... u should stay as close to the model ur
implementing as its possible. ppl using ur class would expect it to
behave acording to their common sense (misleading sometimes though), so
ill advice you to comment any non obvious operators acordingly.

Thanks in advance for your comments

jacob

[Josh Mcfarlane]

jacob navia wrote:

operator >= could be built from ! operator<
operator < could be built from ! operator>=
What guidelines should be sensible to follow?

For guidelines, check the chapter of the FAQ on Operator overloading.
http://www.parashift.com/c++-faq-lite

As for building operations off the inverse of the other operator, you
need to be really careful. Comparisons aren't always what you think.
See http://www.parashift.com/c++-faq-lit...html#faq-29.14 for an
example.

[Greg]

jacob navia wrote:

Hi
I am implementing operator overloading in the context of
the C language.

I would like to have your opinion about this:

Would it be a good idea to assume that the
operator != could be synthethized from

! a == b (operator_equal)

operator >= could be built from ! operator<
operator < could be built from ! operator>=

etc etc.

This would greatly reduce the number of operator
functions that the user needs to implement...

In the same style a == b implies that b == a isn't it?
This means that

int operator==(foo &a,int &b) is the same as
int operator==(int &b,foo &a)

making == and != commutative.

Another step would be to assume commutativity
in the arithmetic operators, what is kind of riskier.

A+B != B+A if you overload the "+" for strings:

"1234" + "5678" --> "12345678", but
"5678" + "1234" --> "56781234"

What guidelines should be sensible to follow?

Thanks in advance for your comments

jacob

Clearly behavior that conforms to the built in operators make the most
sense. C++ however lets the programmer define overloaded operators to
do anything, so it's up to the programmer to show some good sense.

Technically, all the equality and relational operators can be derived
from the less-than operator, <. So just implement operator<() and the
other operators' definitions will be boilerplate.

Greg