Ada Reference Manual — Legal Information

C.4 Preelaboration Requirements

This clause specifies additional implementation and documentation requirements for the Preelaborate pragma (see 10.2.1).

Implementation Requirements

The implementation shall not incur any run-time overhead for the elaboration checks of subprograms and protected_bodies declared in preelaborated library units.

The implementation shall not execute any memory write operations after load time for the elaboration of constant objects declared immediately within the declarative region of a preelaborated library package, so long as the subtype and initial expression (or default initial expressions if initialized by default) of the object_declaration satisfy the following restrictions. The meaning of load time is implementation defined.

Any subtype_mark denotes a statically constrained subtype, with statically constrained subcomponents, if any;

4.1/2

no subtype_mark denotes a controlled type, a private type, a private extension, a generic formal private type, a generic formal derived type, or a descendant of such a type;

any constraint is a static constraint;

any allocator is for an access-to-constant type;

any uses of predefined operators appear only within static expressions;

any primaries that are names, other than attribute_references for the Access or Address attributes, appear only within static expressions;

any name that is not part of a static expression is an expanded name or direct_name that statically denotes some entity;

any discrete_choice of an array_aggregate is static;

no language-defined check associated with the elaboration of the object_declaration can fail.

Documentation Requirements

The implementation shall document any circumstances under which the elaboration of a preelaborated package causes code to be executed at run time.

The implementation shall document whether the method used for initialization of preelaborated variables allows a partition to be restarted without reloading.

Implementation Advice

It is recommended that preelaborated packages be implemented in such a way that there should be little or no code executed at run time for the elaboration of entities not already covered by the Implementation Requirements.