Smart matching for argument constraints

LanX has asked for the wisdom of the Perl Monks concerning the following question:

I'm considering using the smart macht operator for argument constraints at the start of a sub.

I have to admit that ~~ still confuses me a lot

is the following code correct to check if

1. the argument is a simple scalar (that is no ref) 2. and element of the given set (here a b c)?

sub tst {
  %arg = @_;
  
  warn "wrong argument" unless
    "$arg{x}" ~~ [qw/a b c/] ;
}
[download]

so e.g. tst(x => "a"); is ok.

the explicit stringification (quotes) of "$arg{x}" is necessary to avoid tst(x => [qw/a b c/]); to be legal.

Any comments? Any better idioms for checking arguments?

Cheers Rolf

Comment on Smart matching for argument constraints Select or Download Code

Replies are listed 'Best First'.
Re: Smart matching for argument constraints by mithaldu (Monk) on Sep 03, 2012 at 14:30 UTC
You might wish to not use smart match at all, since P5P is intent on making it go away in its current form due to problems like the one you're experiencing.	[reply]
Re^2: Smart matching for argument constraints by LanX (Saint) on Sep 03, 2012 at 14:47 UTC
Thanks, this reflects my general suspicion towards smart matching...! Cheers Rolf	[reply]
Re: Smart matching for argument constraints by tobyink (Canon) on Sep 04, 2012 at 06:53 UTC
Personally I'd make the intent a little more obvious: `warn "wrong argument" if ref $arg{x} \|\| !($arg{x} ~~ [qw/a b c/]);` [download] `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l]