Reduce array to anonymous hash code

Question

Is there anyway to do something like this in perl (convert array hash and use it in one line)?

sub func{
 #from this
 my %args = @_;
 print $args{test};

 #to this
 print %{@_}{test};
}

Im using it for passing errors to callbacks like javascript use strict; use warnings;

sub error{
 my $msg = shift;
 print("ERROR: $msg\n");
}

sub parse_args{
    my %args = @_;
    return $args{args};
}

sub do_something{
   my $args = parse_args(
     args=>{@_},
     optional_args=>["fail_cb"]
   );
   if(!0){
    return(exists $args->{fail_cb} ? $args->{fail_cb}->(err=>"not good") : 0);
   }
}

do_something(
 fail_cb => sub{error(({@_})->{err});}
);

zdim · Accepted Answer · 2017-12-24 01:59:29Z

2

Yes, by making it into a reference and then dereferencing

sub func { say ${{@_}}{key} }

(I must ask, do you really want to be doing this?)

The {@_} creates a hash reference, while ${ ... }{} syntax dereferences it (item 2).

Update to the question edit

Apparently, the intent is to run a callback. But then you need to run that callback

sub func { ${{@_}}{key}->() }

func( key => sub { say "cb here" } );

If you were to print the value, as asked, you'd get the code-reference itself, CODE(0x...)

Or, pass the hashref with a key and (the reference of) arguments for the callback

my $hr = { k1 => sub { .. }, k2 => sub { .. }, .. };
...
func($hr, $key, $arrayref_cb_args);

sub func { $_[0]->{$_[1]}->(@{$_[2]}) }

where now func can decide dynamically what to run. This gives you far more flexibility in design.

For a ready test

perl -wE'
    sub tt { $_[0]->{$_[1]}->(@{$_[2]}) };
    tt( { k1 => sub { say "args: @_" }}, "k1", [qw(cb here)] )
'

prints the line args: cb here

edited Dec 24, 2017 at 1:59

answered Dec 22, 2017 at 5:41

zdim

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7 Comments

TheAschr Over a year ago

Im using like javascript passes errors to callbacks. I will update question to explain.

TheAschr Over a year ago

the main part that I think is ugly is encapsulating the callback within an anonymouse subroutine but from what I can tell, I can't pass a subroutine reference with parameters as the callback ( fail_cb =>\&error(({@_})->{err}) ). This idea is that I can have a subroutine success(),exit(), etc.. that will display the message differently or I can define a completely new one as an anonymose subroutine and still have the err functionality.

TheAschr Over a year ago

The callback is still called within the do_something function in this case and the above code seems to work correctly as far as I can tell.

TheAschr Over a year ago

I think I understand the code (barely) but I am not sure how to apply it to what I'm trying to do. Would the subs defined in $_[0] be error, success, etc..? Also would it make more sense to define $_[0] hash outside tt so that it can be reused with multiple tt calls?

zdim Over a year ago

@TheAschr For example, if you have $rh = { error => sub { say "got error: @_" } }, then yes, func($hr, "error", $cb_args) will run sub { say "...: @_" } with whatever is in arrayref $cb_args. You can have a default for $cb_args refarray so that it's optional.

|

Jim Garrison · Accepted Answer · 2017-12-22 05:41:11Z

1

You can turn it into a hash reference easily with just

{@a}

and dereference entries with, for example

({@a})->{key}

Here's a debugger log:

$ perl -de0

Loading DB routines from perl5db.pl version 1.49_001
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(-e:1):   0
  DB<1> @a = ('a',1,'b',2,'c',3)

  DB<2> x @a
0  'a'
1  1
2  'b'
3  2
4  'c'
5  3
  DB<3> x {@a}
0  'a'
1  1
2  'b'
3  2
4  'c'
5  3
  DB<4> x ({@a})
0  HASH(0x804d82e0)
   'a' => 1
   'b' => 2
   'c' => 3
  DB<5> x ({@a})->{c}
0  3

answered Dec 22, 2017 at 5:41

Jim Garrison

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1 Comment

ysth Over a year ago

The parens are not needed

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