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ABAP Keyword Documentation → ABAP − Reference → Processing Internal Data → Assignments → Assignment and Conversion Rules →Conversions - Performance Note
Conversions in assignments between data objects with different data types, or the specification of a data object in an operand position where a different data type is expected, lead to runtime costs. To avoid these costs, conversions should be avoided where possible and only data objects of the same type should be assigned to one another.
Example
See conversion costs