2012/7/16 Ángel González <keis...@gmail.com>:
>> 1a) If you want to support character classes, you can do it with pcre:
>> http://www.php.net/manual/en/regexp.reference.character-classes.php
> That's more or less what I have thought.
> If it's a string surrounded by square brackets, it's a character class,
> else
> treat as a literal list of characters.
> ] and - can be provided with the old trick of provide "] as first
> character",
> "make - the first or last one".
Right thought. But introducing a new scheme of character-class
identificators or a new kind of describing character-classes is
confusing. As PHP developer I think "Oh no, not again new magic
charsets".
I suggest again to use PCRE for that. The difference to your proposal
is not so big. Examples:
"/[[:alnum:]]/" will return "abc...XYZ0123456789". We can do this also
with "/[a-zA-Z0-9]/". Or "/[a-z0-9]/i". Or "/[[:alpha:][:digit:]]/"
You see: You can do things in much more different ways with PCRE. And
you continue to use this "standard".
[And PCRE supports UTF8. Currently not important. But who knows?]
And maybe we can think about removing the beginning "/[" and the
ending "]/", but a "/" at the end should be optionally possible to add
some regex-parameters (like "/i").
> Having to detect character limits makes it uglier.
Exactly. That's why I think we need not so much magic to the second
parameter. The character-list is just a list of characters. No magic.
We can extent this with a third parameter to tell the function from
which charset it is. And maybe a fourth to tell the random-algorithm,
but I think it's eventually better to have a function for each
algorithm, because that's the way how random currently works.
If I should write it with php this looks like that:
pseudofunction str_random($len, $characters, $encoding = 'ASCII', $algo)
{
$result = '';
$chlen = mb_strlen($characters,$encoding);
for ($i = 0; $i < $len; $i++) {
$result .= mb_substr($characters, myrandom(0, $chlen, $algo),1);
}
return $result;
}
Without testing anything. It's just an idea.
This is a working php-function, but $encoding doesn't work (some
stupid error?) and not using $algo:
function str_random($len, $characters, $encoding = 'ASCII', $algo = null)
{
$result = '';
$chlen = mb_strlen($characters,$encoding);
for ($i = 0; $i < $len; $i++) {
$result .= mb_substr($characters, rand(0, $chlen),1);
}
return $result;
}
> About supporting POSIX classes, that could be cool. But you then need a way
> to enumerate them. Note that isalpha() will be provided by the C
> library, so you
> can't count on having its data. It's possible that PCRE, which we bundle,
> contains the needed unicode tables.
It works without thinking as above written in PHP code, but I dunno if
this could be done in C equally.
>> 3. Because generating a string from character-classes is very handy in
>> general for some other things (many string functions have it), I
>> suggest that it is not part of random_string(). Make a new function
>> str_from_character_class(), or if you use pcre like above
>> pcre_str_from_character_class()?
> How would you use such function? If you want to make a string out of them,
Oh, there are many cases to use it.
For example (I renamed the function to "str_charset()", because it is
just a string of a charset):
// Search spacer strings
strpbrk ("Hello World", str_charset('/[\s]/'));
// remove invisible chars at begin or end (not very much sense,
because a regex in this case is maybe faster)
trim("\rblaa\n", str_charset('/[^[:print:]]/'));
// remove invisible chars: when doing this with very big strings it
could be much faster than with regex.
str_replace(str_split(str_charset('/[^[:print:]]/')), "\rblaa\n");
There are many other more or less useful things you can do with a
charset-string. :)
--
Alex Aulbach
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