ABAP_to_the_Future

Declaring and Creating Variables 2.2
Traditionally, if you created a huge application with locally defined internal tables
and structures and constants and the like and then suddenly realized that you
wanted to reuse a lot of thes e somewhere else, then using a TYPE POOL was the
only way to create such reusable constructs. If you didn’t declare a TYPE POOL ,
then the compiler would complain that your ABAP_TRUE statement was unknown.
Even though the introduction of Z table types in ABAP 6.40 removed part of the
need for TYPE POOLS, they were still used, because there was no other way to have
a globally available constant like ABAP_TRUE. However, as of release 7.02, this is
no longer the case; you can use ABAP_TRUE anywhere you want, and the compiler
will no longer complain. In other words, all existing TYPE POOL statements are
now global.
However, there’s a catch: you’re no longer supposed to create any new TYPE POOL
statements. You may be thinking to yourself, “Why shouldn’t I create TYPE POOLS
any more just because SAP says so?” That ’s a valid question. The answer is that
TYPE POOLS were created to address a specific gap in functionality—a gap which
no longer exists. This is like taking a picture with a Kodak camera or sending a
fax; you could still do these things if you wanted to, but there is no need to do so
any longer.
As it turns out, there is now a solution that deals with both constants and internal
table definitions that have not been crea ted in the form of Z table types: public
type definitions of global Z classes. An example of no longer having to create a Z
table type is when the global class has a public attribute that is a custom table type
defined within the Z class, and the call ing program wants to call a method that
needs that table type passed in. The ca lling program can do something like the
example in Listing 2.11.
DATA: lt_monsters TYPE zcl_monsters=>mtt_monster_table.
zcl_monsters->make_monsters_dance( lt_monsters ).
Listing 2.11 Using a Custom Table Type Declared within a Z Class
This has the advantage that there is now no need to bloat the repository with Z
table types. It is exactly the same with co nstants; if they are a public attribute of
a class, then they can be used anywhere in the system. (In fact, there are standard
SAP classes that contain nothing except constant definitions; you could call them
the younger brothers of TYPE POOLS.)
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