Re: Compile regular expression

[Helmut Eller]

* Cecil Westerhof [2009-12-21 14:03+0100] writes:

> Okay, then in principle I do not have to worry. But one more question. I
> call a function a lot (five million times) with a string containing the
> regular expression. Does the cache work in this case also? Because the
> string is evaluated in the function and looses focus when returning.

That seems to be the most obvious use for a cache.
A simple way to answer such question is to read the source code.  Here
is the condition for cache lookups:

      if (SCHARS (cp->regexp) == SCHARS (pattern)
          && STRING_MULTIBYTE (cp->regexp) == STRING_MULTIBYTE (pattern)
          && !NILP (Fstring_equal (cp->regexp, pattern))
          && EQ (cp->buf.translate, (! NILP (translate) ? translate : 
make_number (0)))
          && cp->posix == posix
          && (EQ (cp->syntax_table, Qt)
              || EQ (cp->syntax_table, current_buffer->syntax_table))
          && !NILP (Fequal (cp->whitespace_regexp, Vsearch_spaces_regexp))
          && cp->buf.charset_unibyte == charset_unibyte)
        break;

As you can see, string-equal is for comparisions.

Helmut