Whats the meaning when variables are enclosed by brackets

Question

Hi,
Whats the meaning when variables are enclosed by brackets?
like say
lv_fieldname(25) TYPE c.
lv_fieldname  = 'Material01'.
what does it mean by saying
ASSIGN (lv_fieldname) TO <fs_fieldname>.

Answer 1

In many statement in ABAP, brackets mean that real "name" of operand (object) will be determined during runtime.
Normally you would write
data lv_fieldname(25) TYPE c VAUE 'SOME_FIELD'.
assign lv_fieldname to <fs>.
write: <fs>.
This code is static . It means that when syntax check takes place, compilator looks for definition of lv_fieldname.
It then assigns value of this field. The resuts is printintg on screen text "SOME_VALUE"
Now you have similar code, but with brackets
data: lv_fieldname(25) TYPE c VAUE 'SOME_FIELD',
         some_field type i vlaue 5.
assign (lv_fieldname) to <fs>.
write: <fs>.
Here code is dynamic . It means that compilator doens't realy know the field name which will be assigned to <fs>.
We told him that this will be determined during runtime ( by means of brackets ) and the real field name we want to assing, is stored in LV_FIELDNAME.
This is equal to writing
assign ('SOME_FIELD') to <fs>.
When program starts, it is no LV_FIELDNAME which is assinged to <fs>, but the field which is stored in LV_FIELDNAME, namely 'SOME_FIELD'.
So the printed result will be 5 .
The same rule with dynamic operands applies i.e. in select statement
data: my_table(5) type c value 'SPFLI'.
select * from (my_table) ...
There is no table in DB named my_table , but compilator "knows" that we don't what to fetch data from MY_TABLE, but we want table name to be determined dynamically (during runtime). So, it is  'SPFLI' table which here will be taken into account.
One more note!
Such dynamic statements are generic (doesn't constitute fixed code) and open new range of possiblities.
Simple extending above example will create flexible (generic) program which can fetch data from different tables with one statement.
parameters: pa_tabname(40) type c.
select * from (pa_tabname) into ....
Of course here you need also dynamic internal table as target area, but this is of no importance here.
Hope this claryfies magic with brackets;)
Regards
Marcin