Re: My very confusing questions

[perlfan]

You are confused because of things that implied in Perl.

Let's back up. You are treating your hash of subroutines like an array of subroutine references. Do you mean to do the following?

my %h = (
  func1 => sub { return sprintf ("0x%x", shift) },
  func2 => sub { return sprintf ("%b", shift) },
  func3 => sub { return sprintf ("%d", shift) },
);

You Then would selectively call the sub you want using using the subroutine reference invocation idiom,

$h{func1}->();

Assuming you do, then the shift operates on @_ - this is the implicit parameters list. For clarity, it is recommended that you unpack parameters, for example:

my %h = (
  func1 => sub { 
    my $value = shift @_;
    return sprintf ("0x%x", $value) 
  },
  func2 => sub { 
    my $value = shift @_;
    return sprintf ("%b", $value); 
},
  func3 => sub { 
    my $value = shift @_;
    return sprintf ("%d", $value); 
},
);

More about shift and why it's used inside of subroutines to unpack parameters:

• shift/unshift operate on the left hand side (LHS) of a list, in this case it is @_
• shift is like pop, but pop operates on the right hand side (RHS) of the list.
• unshift is like push, but push operates on the RHS of the list
• You must use shift on @_ in order to operate on the parameters passed to a subroutine as one traditionally would expect (i.e., Left to Right)

But of course, TIMTOWTDI. Some examples:

Pass in some number of key/value pairs as a simple list

sub foo {
  # requires an even number of parameters in @_
  my %params = @_; 
  return;
}

# to call:

foo(qw/key1 val1 key2 val2 key3 val3/);

As a singular hash reference with some number of key/value pairs already defined

sub foo {
  # get singular hash reference with any number of key/value pairs
  my $params = shift @_; # or alternatively, my $params = $_[0]
  
  # some may want to dereference (I usually don't)

  my %params = %$params;

  return;
}

# to call:

foo( {'key1' => 'val1', 'key2' => 'val2', 'key3' => 'val3' });

# or without braces,

foo( 'key1' => 'val1',  'key2' => 'val2', 'key3' => 'val3' );

I HTH.