Brief comparison between lookup on a varchar2 key
via an index by binary_integer table
and via an index by varchar2 table

Without the associative array, you need to code some hashing by hand...

  ...
  /* using create table t ( idx varchar2(2000), val integer ) */
  type my_lookups_t is table of t.val%type index by binary_integer;

  my_lookups my_lookups_t;
  my_val t.val%type;
  hash_value binary_integer;
  ...
begin
  for j in ( select idx, val from t )

  loop
    hash_value := /* implicit cast to binary_integer */
      Dbms_Utility.Get_Hash_Value (
        name      => j.idx,
        base      => 1000,
        hash_size => 2048 );
    my_lookups ( hash_value ) := j.val;

  end loop;
  ...
  hash_value :=
    Dbms_Utility.Get_Hash_Value (
      name      => 'my current index of interest',
      base      => 1000,
      hash_size => 2048 );
  my_val := my_lookups ( hash_value );

  ...

This fragment can now be simplified thus...

  ...
  type my_lookups_t is table of t.val%type index by varchar2(2000);
  my_lookups my_lookups_t;
  my_val t.val%type;
  ...
begin
  for j in ( select idx, val from t )
  loop

    my_lookups ( j.idx ) := j.val;
  end loop;
  ...  
  my_val := my_lookups ( 'my current index of interest' );
  ...

Not only is the coding simpler, it's more efficient.