Do Not Mutate the Internal Table Currently Being Looped (Iterator Invalidation)

WarningPerformance & Database#EC NO_MOD_LOOP_TABRemote Enabled

Overview

Avoid mutating or sorting tables inside loops.

ATC Finding Messages:

• Do not add, delete, sort, collect, or clear rows from the table currently being looped
• Avoid sorting internal tables inside loops to prevent severe performance degradation

Rationale

Modifying, deleting, inserting, or sorting the internal table currently being traversed inside a LOOP AT itab block invalidates the loop iterator. Sorting during a loop breaks binary search indexes and causes infinite loops or skipped rows. Deleting rows alters sy-tabix dynamically, leading to silent data corruption.

Best Practice: To update row values, use field-symbols (ASSIGNING FIELD-SYMBOL(<row>)) which mutates memory directly in-place without altering table layout. For filtering or structural reshaping, use modern constructor expressions (FILTER #( ... )) or build a new secondary table.

Non-Compliant

" Anti-pattern: Modifying and sorting inside loop invalidates table indexes
LOOP AT lt_items INTO ls_item.
  ls_item-price = ls_item-price * 1.1.
  MODIFY lt_items FROM ls_item.
  SORT lt_items BY item_id.
ENDLOOP.

Compliant

" Clean ABAP: Direct in-place mutation via field symbol without table re-indexing
LOOP AT lt_items ASSIGNING FIELD-SYMBOL(<ls_item>).
  <ls_item>-price = <ls_item>-price * 1.1.
ENDLOOP.

Configuration & Thresholds

This check can be fine-tuned directly in the ATC Check Variant Editor (CHKV) in Eclipse ADT:

Parameter Name	Data Type	Default Value	Description & Guidance
CHECK_APPEND	Boolean	true	Detect APPEND statements targeting the loop table
CHECK_INSERT	Boolean	true	Detect INSERT statements targeting the loop table
CHECK_MODIFY	Boolean	true	Detect MODIFY statements targeting the loop table
CHECK_DELETE	Boolean	true	Detect DELETE statements targeting the loop table
CHECK_CLEAR	Boolean	true	Detect CLEAR or FREE statements targeting the loop table
CHECK_SORT	Boolean	true	Detect SORT statements targeting the loop table
CHECK_SORT_ANY	Boolean	true	Detect SORT statements on any table inside a loop
CHECK_COLLECT	Boolean	true	Detect COLLECT statements targeting the loop table

Suppression

To suppress findings for this rule, append the pseudo-comment to the statement:

" Standard pseudo-comment:
... "#EC NO_MOD_LOOP_TAB

" SAP CI_ prefix format:
... "#EC CI_NO_MOD_LOOP_TAB

Related Rules

• Avoid String Concatenation Inside Loops (Quadratic Memory Allocation) — #EC NO_CONCAT_LOOP
• Only Modify Tables Defined in Your Own Package/Component — #EC NO_MOD_STD_TABLE
• Specify TRANSPORTING in Internal Table MODIFY and READ Operations — #EC PREF_TRANSPORT

Technical Details

• Native ATC Class: ZCL_SKYLINT_NO_MOD_LOOP_TAB
• Implementation File: zcl_skylint_no_mod_loop_tab.clas.abap