Why is split(' ') trying to be (too) smart?

Question

I just discovered the following odd behavior with String#split:

"a\tb c\nd".split
=> ["a", "b", "c", "d"]

"a\tb c\nd".split(' ')
=> ["a", "b", "c", "d"]

"a\tb c\nd".split(/ /)
=> ["a\tb", "c\nd"]

The source (string.c from 2.0.0) is over 200 lines long and contains a passage like this:

/* L 5909 */
else if (rb_enc_asciicompat(enc2) == 1) {
    if (RSTRING_LEN(spat) == 1 && RSTRING_PTR(spat)[0] == ' '){
        split_type = awk;
    }
}

Later, in the code for the awk split type, the actual argument isn't even used any more and does the same as a plain split.

• Does anyone else feel that this is somehow broken?
• Are there good reasons for this?
• Does “magic” like that happen more often than most people might think in Ruby?

Answer 1

It's consistent with Perl's split() behavior. Which in turn is based on Gnu awk's split(). So it's a long-standing tradition with origins in Unix.

From the perldoc on split:

As another special case, split emulates the default behavior of the command line tool awk when the PATTERN is either omitted or a literal string composed of a single space character (such as ' ' or "\x20" , but not e.g. / / ). In this case, any leading whitespace in EXPR is removed before splitting occurs, and the PATTERN is instead treated as if it were /\s+/ ; in particular, this means that any contiguous whitespace (not just a single space character) is used as a separator. However, this special treatment can be avoided by specifying the pattern / / instead of the string " " , thereby allowing only a single space character to be a separator.

Answer 2

Check out the documentation, this part in particular:

If pattern is a String, then its contents are used as the delimiter when splitting str. If pattern is a single space, str is split on whitespace, with leading whitespace and runs of contiguous whitespace characters ignored.

If pattern is omitted, the value of $; is used. If $; is nil (which is the default), str is split on whitespace as if ` ‘ were specified.

You can use a regexp to split the string.