On 06/20/2017 10:59 AM, Martin Sebor wrote:
On 06/20/2017 02:41 AM, Aldy Hernandez wrote:
On 05/23/2017 03:26 PM, Martin Sebor wrote:
On 05/23/2017 04:48 AM, Aldy Hernandez wrote:
+ void Union (wide_int x, wide_int y);
+ bool Union (const irange &r);
+ bool Union (const irange &r1, const irange &r2);
+
+ // THIS = THIS ^ [X,Y]. Return TRUE if result is non-empty.
+ bool Intersect (wide_int x, wide_int y, bool readonly = false);
+ // THIS = THIS ^ R. Return TRUE if result is non-empty.
+ // THIS = R1 ^ R2. Return TRUE if result is non-empty.
+ bool Intersect (const irange &r1, const irange &r2, bool readonly =
false);
+ // Return TRUE if THIS ^ R will be non-empty.
+ bool Intersect_p (const irange &r)
+ { return Intersect (r, /*readonly=*/true); }
I would suggest the following changes to Union, Intersect, and Not:
1) Define all three members without the readonly argument and
returning irange& (i.e., *this). The return value can be
used wherever irange& is expected, and the is_empty() member
function can be called on it to obtain the same result. E.g.,
Intersect A with B, storing the result in A:
irange A, B;
if (A.Intersect (B).is_empty ()) { ... }
2) Add non-members like so:
irange range_union (const irange &lhs, const irange &rhs)
{
return irange (lhs).Union (rhs);
}
and find out if the union of A or B is empty without modifying
either argument:
irange A, B;
if (range_union (A, B).is_empty ()) { ... }
Perhaps we could provide an implicit conversion from irange to bool such
that we could write:
if (range_union (A, B)) { ... }
as well as being able to write:
if (!range_union (A, B).is_empty ()) { ... }
That is, have range_union() return an irange as suggested, but have a
bool overload (or whatever the C++ nomenclature is) such that converting
an irange to a bool is interpreted as ``nitems != 0''.
Is this acceptable C++ practice?
Implicit conversion to bool is a common way of testing validity
but I don't think it would be too surprising to use it as a test
for non-emptiness. An alternative to consider is to provide
an implicit conversion to an unsigned integer (instead of
num_ranges()(*)) and have it return the number of ranges. That
will make it possible to do the same thing as above while also
simplifying the API.
I really like this.
I have added an implicit conversion to unsigned that returns the number
of sub-ranges. However, I have also left the empty_p() method for a
cleaner interface within the class itself. It feels wrong to type "if
(!*this)" to represent emptiness within the class.
Martin
[*] FWIW, there's nothing wrong with the name num_ranges() but
those familiar with the C++ standard library are going to be
accustomed to size() as the name of a function that returns
the number of elements in a container. Since the irange class
is an ordered sequence of ranges, size() would work for it too.
In my upcoming patch I have renamed num_ranges() to num_pairs() which I
thought was clearer, but if you still feel strongly about this, I can
rename to size().
PS Thinking of the irange class as a container of ranges suggests
the design might benefit from introducing a simple lower-level
abstraction (class) for a single contiguous range.
Hmmm, indeed. Perhaps when the dust settles with the patch I'm about to
post :).
Thanks for your suggestions.
Aldy
