use strict;

  my %hash = ();
  foreach $value (@some_list) {
    my $key = make_some_key($value);
    $hash{$key} = $value;
  }
[download]

In other words, just assign a new key/value pair using $hash{$key} = $value. It's the logical compliment of how you'd access a hash value: $value = $hash{$key}

-Ted