Chapter 7: Portability - TOC - 7.6 REPRESENTATION CLAUSES AND IMPLEMENTATION-DEPENDENT FEATURES

7.6.6 Unchecked Deallocation

guideline

Avoid dependence on Ada.Unchecked_Deallocation (see Guideline 5.9.2).

rationale

The unchecked storage deallocation mechanism is one method for overriding the default time at which allocated storage is reclaimed. The earliest default time is when an object is no longer accessible, for example, when control leaves the scope where an access type was declared (the exact point after this time is implementation-dependent). Any unchecked deallocation of storage performed prior to this may result in an erroneous Ada program if an attempt is made to access the object.

This guideline is stronger than Guideline 5.9.2 because of the extreme dependence on the implementation of Ada.Unchecked_Deallocation. Using it could cause considerable difficulty with portability.

notes

Ada.Unchecked_Deallocation is a supported feature in all Ada implementations. The portability issue arises in that unchecked storage deallocations might cause varying results in different implementations.

exceptions

Using unchecked deallocation of storage can be beneficial in local control of highly iterative or recursive algorithms where available storage may be exceeded.