Dynamic Semantics (GNAT Reference Manual) (original) (raw)

17.2.2.3 Dynamic Semantics ¶

The evaluation of a delta_aggregate begins with the evaluation of thebase_expression of the delta_aggregate; then that value is used to create and initialize the anonymous object of the aggregate. The bounds of the anonymous object of an array_delta_aggregate and the discriminants (if any) of the anonymous object of a record_delta_aggregate are those of thebase_expression.

If a record_delta_aggregate is of a specific tagged type, its tag is that of the specific type; if it is of a class-wide type, its tag is that of the base_expression.

For a delta_aggregate, for each discrete_choice or each subcomponent associated with a record_subcomponent_associated,array_component_association or array_subcomponent_association (in the order given in the enclosing discrete_choice_list orsubcomponent_association_list, respectively):

• if the associated subcomponent belongs to a variant, a check is made that the values of the governing discriminants are such that the anonymous object has this component. The exception Constraint_Error is raised if this check fails.
• if the associated subcomponent is a subcomponent of an array, then for each represented index value (in ascending order, if the discrete_choicerepresents a range):

  • the index value is converted to the index type of the array type.
  • a check is made that the index value belongs to the index range of the corresponding array part of the anonymous object; Constraint_Error is raised if this check fails.
  • the expression of the record_subcomponent_association,array_component_association or array_subcomponent_association is evaluated, converted to the nominal subtype of the associated subcomponent, and assigned to the corresponding subcomponent of the anonymous object.