Aldy Hernandez <al...@redhat.com> writes:
> 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.
Conversions to bool and conversions to int both seem dangerous.
E.g. people might try "range1 | range2" as a shorthand for taking the
union of the ranges. It'll compile but instead give the bitwise OR
of the two range counts.
How about instead having helper functions like intersect_p,
as for bitmaps?
Thanks,
Richard
