Expression Logging

In two preceding blogs I bragged about CL_DEMO_OUTPUT.

Predictably, there is some disappointment because this class is not intended for productive usage.

Fair enough. But you can use it for testing purposes.

As an example, I will show you how you can use CL_DEMO_OUTPUT to produce a logfile for an expression. Quick and dirty.

To do so I choose the following simple constructor expression.

TYPES itab TYPE STANDARD TABLE OF i WITH EMPTY KEY.

DATA(itab) =
  VALUE itab(
    FOR i = 1 UNTIL i > 3
    FOR j = 1 UNTIL j > 3
      ( i * 10 + j ) ).

Of course, you can test the result with cl_demo_output=>display( itab ).

But assume that you want to know what happens inside the expression and it is a more complicated expression and you don’t want to debug or you can’t or don’t want to use other convenience tools (watchpoint, logpoints) provided by the ABAP Workbench/ADT or whatsoever.

In that situation you can instrumentalize an expression with CL_DEMO_OUTPUT, e.g. by misusing a LET expression:

TYPES itab TYPE STANDARD TABLE OF i WITH EMPTY KEY.

DATA(log) = cl_demo_output=>new( ).

 DATA(itab) =
  VALUE itab(
    FOR i = 1 UNTIL i > 3
    FOR j = 1 UNTIL j > 3 
    LET o = log->write( |{ i }, { j }\n{ i * 10 + j } | )->line( ) IN
      ( i * 10 + j ) ).

log->display( ).

Adding these three temporary lines to the above code gives:

Note that the local variable o declared behind LET is not used at all. It simply serves as hook for writing into the output object referenced by log.

There are no limits to the imagination!