[phobos] std.array.ilength

[Michel Fortin]

I don't know, but having both length and ilength seems like it could be confusing. I mean, how can you answer simply to a question about which should be used?

It seems like there's two criteria to consider when answering this question: whether you prefer a 32-bit fixed value (useful storing a lot of them, not useful for local variables) and whether you want to use a signed value (useful to avoid some issues when substracting indices). What if you only need one of these two things?

Le 2011-02-17 à 17:28, Andrei Alexandrescu a écrit :

> I assume I'm in the minority here, but I don't see a need for such a function.
> 
> Andrei
> 
> On 2/17/11 1:40 PM, David Simcha wrote:
>> Fair points.  You've convinced me (since I didn't have a very strong
>> opinion before).  Let's go with int.  I've also come to believe that
>> ilength is the best name because it's negligible extra typing compared
>> to .length, so people will actually use it.  Proposed function for
>> inclusion in object:
>> 
>> /**
>> Returns the length of an array as a 32-bit signed integer.  Verifies
>> with an assert that arr.length <= int.max unless this can be proven
>> at compile time.  This is a useful shortcut for getting the
>> length of a arrays that cannot plausibly have length longer than
>> int.max (about 2 billion) as a 32-bit integer even if building
>> for a 64-bit target.  It's also useful for converting an array length
>> to a signed integer while verifying the safety of this
>> conversion if asserts are enabled.
>> */
>> @property int ilength(T)(const T[] arr) pure nothrow @safe {
>>     static if(size_t.sizeof > uint.sizeof || T.sizeof == 1) {
>>         assert(arr.length <= int.max,
>> "Cannot get integer length of array with >int.max elements."
>>         );
>>     }
>> 
>>     return cast(int) arr.length;
>> }
>> 
>> 
>> On Thu, Feb 17, 2011 at 2:24 PM, Don Clugston <dclugston at googlemail.com
>> <mailto:dclugston at googlemail.com>> wrote:
>> 
>>    On 17 February 2011 17:10, David Simcha <dsimcha at gmail.com
>>    <mailto:dsimcha at gmail.com>> wrote:
>>     > Can you elaborate on why?  Unsigned seems like the perfect type
>>    for an array
>>     > length.
>> 
>>    An array length is a positive integer, you want to treat it as an
>>    integer, not as a bag of bits.
>>    Using an unsigned types is like using a cast, to be avoided whenever
>>    possible. They're a breeding ground for bugs,
>>    and a disturbingly large fraction of programmers don't understand them.
>> 
>> 
>> 
>>    On 17 February 2011 18:02, David Simcha <dsimcha at gmail.com
>>    <mailto:dsimcha at gmail.com>> wrote:
>>     > My main gripe with going with int is that it eliminates the
>>    possibility of
>>     > making ilength() a noop that just returns .length on 32.  The
>>    assert would
>>     > still be necessary.
>> 
>>    But the assert adds value.
>>    Note that an assert is only required on arrays of size 1 --  ubyte,
>>    byte, char.
>>    On everything else, it's still a no-op.
>> 
>> 
>>     > On Thu, Feb 17, 2011 at 9:48 AM, Don Clugston
>>    <dclugston at googlemail.com <mailto:dclugston at googlemail.com>>
>>     > wrote:
>>     >>
>>     >> On 17 February 2011 14:59, David Simcha <dsimcha at gmail.com
>>    <mailto:dsimcha at gmail.com>> wrote:
>>     >> > Hey guys,
>>     >> >
>>     >> > Kagamin just came up with a simple but great idea to mitigate the
>>     >> > pedantic
>>     >> > nature of 64-bit to 32-bit integer conversions in cases where
>>    using
>>     >> > size_t
>>     >> > doesn't cut it.  Examples are storing arrays of indices into other
>>     >> > arrays,
>>     >> > where using size_t would be a colossal waste of space if it's
>>    safe to
>>     >> > assume
>>     >> > none of the arrays will be billions of elements long.
>> 
>> 
>>     >> >  int or uint?  I used int only b/c that was the example on the
>>     >> > newsgroup,
>>     >> > but I think uint makes more sense.
>>     >>
>>     >> I *strongly* oppose uint. We should take every possible
>>    opportunity to
>>     >> reduce usage of unsigned numbers.
>>     >> 'i' implies immutable.
>>     >> How about intlength  (or intLength ?)
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>> 
>> 
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Michel Fortin
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http://michelf.com/