Re: [boost] compare
[EMAIL PROTECTED] writes: Hey Jan - First off, let me say: excellent idea! Several times I've wanted just such a class, and I would be happy to see this added to Boost. I have a few suggestions/things to consider: 1) Instead of operator bool, use the unspecified-bool-type discussed elsewhere on this list; it's safer. Yup. 2) I'm not sure that the choice of the name is ideal. OTOH, I can't think of a better one... lexicographic? 3) I'd like to see a general solution for this problem using real (late-bound) function objects as well, if you know what I mean. This would be a lot harder, though, so maybe it should be put on a wish-list. Have you given any thought to this approach? return compare.less(p1.x, p2.x) .greater(p1.y, p2.y) .call(f, p1.z, p2.z); ?? Just one dumb idea for a comparison DSL... - Dave Abrahams Boost Consulting www.boost-consulting.com ___ Unsubscribe other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
RE: [boost] compare
-Original Message- From: David Abrahams [mailto:[EMAIL PROTECTED] [EMAIL PROTECTED] writes: 3) I'd like to see a general solution for this problem using real (late-bound) function objects as well, if you know what I mean. This would be a lot harder, though, so maybe it should be put on a wish-list. Have you given any thought to this approach? return compare.less(p1.x, p2.x) .greater(p1.y, p2.y) .call(f, p1.z, p2.z); ?? Sorry, I wasn't very clear. I mean defining a compare_t that could be used something like: compare_tposition::x, position::y, position::z that would result in a function object type that produced the same behaviour when given two arguments of type 'position'. (Usable, e.g., as a template argument to std::set). I don't see any way of supporting that simple of a syntax, though; the nicest I can see is: compare_typeposition, compare_tdouble, position::x, compare_tdouble, position::y, compare_tdouble, position::z which is pretty hideous. :( -Steve ___ Unsubscribe other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
RE: [boost] compare
-Original Message-
From: Jan Langer [mailto:[EMAIL PROTECTED]
Just one other thing - instead of:
enum result { minus, zero, plus };
I would do:
enum result { minus = -1, zero, plus };
just for the sake of code readability and ease of understanding. It doesn't
change the logic at all.
-Steve
___
Unsubscribe other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
[boost] compare
hi,
for several times i used a small utility class, so i thought it might be
interesting for boost too.
it takes pairs of arguments and compares them pairwise beginning with
the first one.
an example usage would be a special sorting operators:
struct position
{
double x, y, z;
};
bool operator (position const p1, position const p2)
{
return compare (p1.x, p2.x)
(p1.y, p2.y)
(p1.z, p2.z);
}
is equal to
bool operator (position const p1, position const p2)
{
if (p1.x == p2.x)
if (p1.y == p2.y)
return p1.z p2.z;
else
return p1.y p2.y;
else
return p1.x p2.x;
}
or
struct person
{
std::string firstname, lastname;
};
bool operator (person const p1, person const p2)
{
return compare
(p1.lastname, p2.lastname, cmp_case_insensitive)
(p1.firstname, p2.firstname, cmp_case_insensitive);
}
where cmp_case_insensitive is a comparision function which is used
instead of operator to compare the arguments.
the class itself is quite short:
class compare
{
enum result { minus, zero, plus };
public:
compare () : v_ (zero) {}
template typename T
compare (T const a, T const b)
: v_ (compare () (a, b).v_)
{}
template typename T, typename Cmp
compare (T const a, T const b, Cmp cmp)
: v_ (compare () (a, b, cmp).v_)
{}
template typename T
compare operator () (T const a, T const b)
{
if (v_ == zero)
{
if (a b)
v_ = plus;
else if (b a)
v_ = minus;
else
v_ = zero;
}
return *this;
}
template typename T, typename Cmp
compare operator () (T const a, T const b, Cmp cmp)
{
if (v_ == zero)
{
if (cmp (a, b))
v_ = plus;
else if (cmp (b, a))
v_ = minus;
else
v_ = zero;
}
return *this;
}
operator bool ()
{
return v_ == plus;
}
private:
result v_;
};
--
jan langer ... [EMAIL PROTECTED]
pi ist genau drei
___
Unsubscribe other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
