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digitalmars.D.bugs - [Issue 5977] New: String splitting with empty separator

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5977

           Summary: String splitting with empty separator
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: patch
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2011-05-10 16:30:55 PDT ---
This D2 program seems to go in infinte loop (dmd 2.053beta):


import std.string;
void main() {
    split("a test", "");
}

------------------------

My suggestion is to add code like this in std.array.split():

if (delim.length == 0)
    return split(s);

This means that en empty splitting string is like splitting on generic
whitespace. This is useful in code like:

auto foo(string txt, string delim="") {
    return txt.split(delim);
}


This means that calling foo with no arguments splits txt on whitespace,
otherwise splits on the given string. This allows to use the two forms of split
in foo() without if conditions. This is done in Python too, where None is used
instead of an empty string.


The modified split is something like (there is a isSomeString!S2 because are
special, they aren't generic arrays, splitting on whitespace is meaningful for
strings only):


Unqual!(S1)[] split(S1, S2)(S1 s, S2 delim)
if (isForwardRange!(Unqual!S1) && isForwardRange!S2)
{
    Unqual!S1 us = s;
    if (isSomeString!S2 && delim.length == 0)
    {
        return split(s);
    }
    else
    {
        auto app = appender!(Unqual!(S1)[])();
        foreach (word; std.algorithm.splitter(us, delim))
        {
            app.put(word);
        }
        return app.data;
    }
}


Beside this change, I presume std.algorithm.splitter() too needs to test for an
empty delim.

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--- Comment #1 from bearophile_hugs eml.cc 2011-09-25 08:16:21 PDT ---
Alternative: throw an ArgumentError("delim argument is empty") exception if
delim is empty.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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monarchdodra gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel350 bigpond.com


--- Comment #2 from monarchdodra gmail.com 2012-10-22 02:42:42 PDT ---
*** Issue 8551 has been marked as a duplicate of this issue. ***

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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monarchdodra gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |monarchdodra gmail.com
         AssignedTo|nobody puremagic.com        |monarchdodra gmail.com


--- Comment #3 from monarchdodra gmail.com 2012-10-22 02:52:16 PDT ---
(In reply to comment #0)

 This D2 program seems to go in infinte loop (dmd 2.053beta):
 
 
 import std.string;
 void main() {
     split("a test", "");
 }
 
 ------------------------
 
 My suggestion is to add code like this in std.array.split():
 
 if (delim.length == 0)
     return split(s);
 
 This means that en empty splitting string is like splitting on generic
 whitespace. This is useful in code like:
 
 auto foo(string txt, string delim="") {
     return txt.split(delim);
 }


I think it is a bad idea on two counts:

1. If the user wanted that behavior, he'd have written it as such. If the user
actually passed a seperator that is an empty range, he probably didn't mean for
it split by spaces.

2. I think it would also bring a deviation of behavior between strings and
non-strings. Supposing r is empty:
* "hello world".split(""); //Ok, split white
* [1, 2].split(r); //Derp.

(In reply to comment #1)

 Alternative: throw an ArgumentError("delim argument is empty") exception if
 delim is empty.


I *really* think that is a *much* saner approach. Splitting with an empty
separator is just not logic. Trying to force a default behavior in that
scenario is wishful thinking (IMO).

I think it should throw an error. I'll implement this.

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prev sibling parent d-bugmail puremagic.com writes:
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hsteoh quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hsteoh quickfur.ath.cx


--- Comment #4 from hsteoh quickfur.ath.cx 2013-01-03 20:28:42 PST ---
FWIW, in perl, splitting on an empty string simply returns an array of
characters. I think that better reflects the symmetry of join("", array).

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