"String calculation not permitted here" is thrown on REDUCE-CodePudding

I have a few field names in LT_FIELDS. I am trying to concatenate the data in that internal table in a specific format and append it to LT_WHERE for a dynamic select query.

Below is the snippet I wrote:

TYPES: BEGIN OF ty_whr,
         fieldname TYPE string,
       END OF ty_whr.

DATA(lt_fields) = VALUE rsds_frange_t( ).
DATA(lt_where) = REDUCE ty_whr(
                   INIT whereclause = VALUE ty_whr( )
                   FOR <fields> IN lt_fields
                   NEXT whereclause = 
                     COND #( WHEN whereclause IS NOT INITIAL
                             THEN <fields>-fieldname && | IN | && |@| && <fields>-fieldname && | AND |
                             ELSE <fields>-fieldname && | IN | && |@| && <fields>-fieldname
                          ) ).

I am getting this error on concatenation part:

String calculation not permitted here

Is the syntax wrong here?

CodePudding user response：

The syntax messages are a little bit strange with Constructor Expressions.

In fact the issue is due to the target (whereclause) which is a structure, you can't assign a Text Literal to a structure, instead you should assign it to its text component whereclause-fieldname (right after NEXT):

TYPES: BEGIN OF ty_whr,
         fieldname TYPE string,
       END OF ty_whr.

DATA(lt_fields) = VALUE rsds_frange_t( ).
DATA(lt_where) = REDUCE ty_whr(
                   INIT whereclause = VALUE ty_whr( )
                   FOR <fields> IN lt_fields
                   NEXT whereclause-fieldname = 
                     COND #( WHEN whereclause IS NOT INITIAL
                             THEN <fields>-fieldname && | IN | && |@| && <fields>-fieldname && | AND |
                             ELSE <fields>-fieldname && | IN | && |@| && <fields>-fieldname
                          ) ).