Re: [PATCH 5.005_63] Open-ended slices: (a..z)[23..]

[John Macdonald <jmm@pickering.elegant.com>]

Mark-Jason Dominus <mjd@plover.com> writes:
|| I didn't mention it on speculation.  I mentioned it because I have
|| relied on it.
|| 
|| Simon sais the same thing, and I don't think it is as unlikely as
|| either of you seem to think.
|| 
|| Other times this has come up, I've noticed that there seem to be two
|| sorts of people involved in the debate.  For some people, it is an
|| abnormal discontinuity that ($x..$y) yields the empty list when $y<$x.
|| For others, it seems perfectly normal.
|| 
|| The first group of people cannot imagine that anyone would ever
|| actually make use of such an abnormal discontinuity.  The second group
|| finds it perfectly normal.

I also have code that computes end points and then uses them,
comfortable in the knowledge that a null list (where the
computed $x is greater than the computed $y) just quietly does
nothing.

    # (binsearch returns index of first element that is >= the
    # specified value)
    $start_index = binsearch( $array, $start_value );
    $past_end_index = binsearch( $array, $end_value+1 );
    foreach( @{$array}[ $start_index .. $end_index-1 ] ) {
        # ...
    }

Often, these index positions are collected "in passing" during an
examination of the array done for another purpose.

    $start_index = @$array;
    $end_index = -1;
    while( ... ) {
        # ...
        
        # interesting parts of $array are examined, current index is $index
        $start_index = $index
            if $index < $start_index && $array->[$index] >= $start_value;
        $end_index = $index
            if $index > $end_index && $array->[$index] <= $end_value;
        
        # ...
    }
    
    foreach( @{$array}[ $start_index .. $end_index ] ) {
        # ...
    }

--
John Macdonald     jmm@jmm.pickering.elegant.com

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