Perl programming: continue block

I have just started learning Perl scripting language and have a question.

In Perl, what is t开发者_运维百科he logical reason for having continue block work with while and do while loops, but not with for loop?

From http://perldoc.perl.org/functions/continue.html

If there is a continue BLOCK attached to a BLOCK (typically in a while or foreach ), it is always executed just before the conditional is about to be evaluated again, just like the third part of a for loop in C.

Meaning that in the for loop, the third argument IS the continue expression, e.g. for (initialization; condition; continue), so therefore it is not needed. On the other hand, if you use for in the foreach style, such as:

for (0 .. 10) {
    print "$i\n";
} continue { $i++ }

It will be acceptable.

I suspect that the continue block isn't used in for loops since it is exactly equivalent to the for loop's 3rd expression (increment/decrement, etc.)

eg. the following blocks of code are mostly equivalent:

for ($i = 0; $i < 10; $i++)
{
}

$i = 0;
while ($i < 10)
{
}
continue
{
    $i++;
}

You can use a continue block everywhere it makes sense: with while, until and foreach loops, as well as 'basic' blocks -- blocks that aren't part of another statement. Note that you can use the keyword for instead of foreach for the list iteration construct, and of course you can have a continue block in that case.

As everybody else said, for (;;) loops already have a continue part -- which one would you want to execute first?

continue blocks also don't work with do { ... } while ... because syntactically that's a very different thing (do is a builtin function taking a BLOCK as its argument, and the while part is a statement modifier). I suppose you could use the double curly construct with them (basic block inside argument block), if you really had to:

do {
    {
        ...;
        continue if $bad;
        ...;
    }
    continue {
        ...; # clean up
    }
} while $more;