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Siemel Naran
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 Posted: Thu Jun 26, 2003 2:22 pm Post subject: Re: can i overload operator< to get (a < b < c) |
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"Geir Bjarte Terum" <clcppm-poster (AT) this (DOT) is.invalid> wrote
| Quote: | Yes it is possible to overload the operator < for any type including
built
in types. But one must be willing to add a statement controller.
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Really? I thought in overloaded operator<(T,U) either T or U or both
should
be class types -- in other words, not builtin types.
--
+++++++++++
Siemel Naran
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]
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Geir Bjarte Terum
Guest
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| Posted: Thu Jun 26, 2003 6:56 pm Post subject: Re: can i overload operator< to get (a < b < c) |
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Geir Bjarte Terum wrote:
| Quote: | [snip]
#define IF(expr) if (eval << expr)
#define WHILE(expr) while (eval << expr)
#define EVAL(expr) (eval << expr)
Now you can write:
IF (a < b < c) { }
WHILE (a < b < c) { }
cout << EVAL(a < b < c) << endl;
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James Kanze wrote:
(ref. news:d6652001.0306240329.50ce627f (AT) posting (DOT) google.com)
| Quote: |
Since macros aren't evaluated recursively, you can even write:
#define if( expr ) if ( eval << expr )
etc.
It's interesting to note that with this, something like:
if ( condition() && a < b < c ) ...
and
if ( a < b < c && condition() ) ...
could give different results.
This sounds like a good candidate for the obfuscated C++ contest.
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Yes it is generally a bad idea to remove the information
contained in using upper letters for the IF macro etc.
And it is especially a bad idea when we have a case as
you describe in your example. A such declaration is
not only a good candidate for the obfuscated C++
contest, but is also potentially fatal as long as the
macro have special conditions of usage attached,
as your example suggest.
---
Geir Bjarte Terum
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]
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Geir Bjarte Terum
Guest
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| Posted: Fri Jun 27, 2003 11:01 am Post subject: Re: can i overload operator< to get (a < b < c) |
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Geir Bjarte Terumwrote:
| Quote: | Yes it is possible to overload the operator < for any type including
built in types. But one must be willing to add a statement controller.
[ref. news:wPqJa.1515$os2.21179 (AT) news2 (DOT) e.nsc.no]
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Siemel Naran wrote:
| Quote: | Really? I thought in overloaded operator<(T,U) either T or U
or both should be class types -- in other words, not builtin types.
|
In operator overloading at least one of the operator operands
must be a UDT. By using a statement controller, or more
presise - an expression evaluator, the left operand is a UDT
and which enable the programmer to get in control - even
for builtin types.
Example of overloading an int operator using an expression
evaluator:
class int_evaluator
{
int value;
public:
explicit int_evaluator(int value) : value(value) { }
bool operator < (int rhs) const
{
return value < rhs;
}
// ... other overloaded operators ...
};
struct evaluator
{
int_evaluator operator << (int rhs)
{
return int_evaluator(rhs);
}
};
evaluator eval;
#define IF(expr) if (eval << expr)
---
Geir Bjarte Terum
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]
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