Comprehensive and Detailed Explanation From Exact Extract:

RAP and ABAP Cloud emphasize expression-based coding, and REDUCE is a key reduction expression. The code above defines an accumulator (h_structure_variable) and iterates over an internal table (source_itab) with FOR … IN …, so a loop over the source table is created (D). In each iteration, fields are accumulated and, when the expression finishes, the final accumulator value is returned and assigned to structure_variable. With compatible structured types, components are copied name-by-name (C).

In ABAP Cloud, the language is explicitly described as “aligned and extended to support RAP … The application developer uses typed APIs … and benefits from static code checks.” This underpins the use of typed, expression-based constructs like REDUCE for safe, declarative logic.