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Nesting Depth

Other versions: 7.31 | 7.40 | 7.54

Background

The nesting depth is the number of statement blocks that are nested due to the use of control structures (branches, loops). We will discuss the nesting depth at the level of a procedure (method). Implementations must not occur at other points.

The maximum nesting depth is restricted to 256 by the ABAP Compiler.

Rule

Restrict the nesting depth of control structures

Restrict the maximum nesting depth within a procedure (method) to five levels.

Details

In addition to the number of executable statements, the control structures of a procedure (method) are also important for their clarity and traceability. Nested branches and loops (IF, CASE, DO, WHILE, LOOP statements, etc.) become less clear and more difficult to trace with every nesting level. For this reason, the nesting depth must be restricted within a procedure, for example, by moving functionality to other procedures.

A maximum nesting depth of five levels is considered tolerable. A deeper nesting requires a great deal of effort to trace the program flow based on the source code. This would considerably constrain maintenance and further development.

Note

The use of modern language elements can help to restrict the maximum nesting depth. This is the case if a statement or a predefined function replaces an entire control structure, for instance, for REPLACE with the ALL OCCURRENCES addition or for the numerical extremum functions, nmax( ) and nmin( ), to determine the maximum or minimum value. The former replaces a loop, the latter an IF control structure.

Example

The transition from the bad to the good example in the rule for modern ABAP shows how you can reduce the nesting depth by using modern language elements.