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Re: Understanding the benefit of Given/When ...

by ikegami (Pope)
on Mar 04, 2010 at 15:14 UTC ( #826720=note: print w/replies, xml ) Need Help??

in reply to Understanding the benefit of Given/When ...

The when has an automatically built in smart match ~~. Nice ...but how can I take profit from this smart match if the parameter passed into given can only be a scalar?

Maybe, but you can check that scalar against a variety of things, not all of them scalars.

use 5.010; use strict; use warnings; my @x = qw( abc def ); given ("abc") { when (@x) { print "when\n"; } default { print "default\n"; } }

I have no idea what you are asking.

Replies are listed 'Best First'.
Smart enough for Smart Match??? (was "Understanding ...Given/When" )
by LanX (Chancellor) on Mar 04, 2010 at 15:53 UTC
    > I have no idea what you are asking.

    Maybe I'm not smart enough for Smart Match ;)

    It seems that the operands in Smart Match are swapped to what I expected after reading the docs

    Is perlsyn#Switch statements clear???

    Most of the power comes from implicit smart matching: when($foo) is exactly equivalent to when($_ ~~ $foo)
    ($_ was given)


    # $a $b Type of Match Implied Matching Code # ====== ===== ===================== ============= ... # Array Regex array grep grep /$b/, @$a
    see perlsyn#Smart matching in detail

    so when writing

    given (@a) { when (/abc/) {} }

    I expect this to be tested:  @a ~~ /$b/ in the meaning of  grep /$b/, @$a

    Two possibilities:

    a) the docs need a rewrite!

    b) my brain needs a rewrite! ;)

    Cheers Rolf ...still confused...

    UPDATE: Sorry personally I think that ~~ is far too overloaden with functionality to be easily understood!!!

      I don't know why the following doesn't work:
      use 5.010; use strict; use warnings; my @a='abc'; given (@a) { when (/abc/ ) { print "abc\n" } when (1 ) { print "#\n" } when (['abc']) { print "copy\n" } when (\@a ) { print "self\n" } } # copy
      Why is it skipping Array Regex to go to Array Array?
        Have a look at the last code in the OP (I updated it 10 minutes after posting)

        given(@array) and given(\@array) both produce the same ref in $_, but the smartmatch doesn't work as documented.

        While I can understand why to limit given to simple scalars I think the docs should either be updated to reflect this behaviour or it's a bug.

        UPDATE: you should add continues to se which clauses are true

        my @a=('abc',1); given (@a) { when (/abc/ ) { print "abc\n" ;continue} when (1 ) { print "#\n" ;continue} when (['abc',1]) { print "copy\n" ;continue} when (\@a ) { print "self\n" } }


        Argument "abc" isn't numeric in smart match at /home/lanx/tmp/ike_give line 9. # copy self

        Cheers Rolf

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