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2.121 Pragma No_Tagged_Streams


pragma No_Tagged_Streams [([Entity =>] tagged_type_LOCAL_NAME)];

Normally when a tagged type is introduced using a full type declaration, part of the processing includes generating stream access routines to be used by stream attributes referencing the type (or one of its subtypes or derived types). This can involve the generation of significant amounts of code which is wasted space if stream routines are not needed for the type in question.

The No_Tagged_Streams pragma causes the generation of these stream routines to be skipped, and any attempt to use stream operations on types subject to this pragma will be statically rejected as illegal.

There are two forms of the pragma. The form with no arguments must appear in a declarative sequence or in the declarations of a package spec. This pragma affects all subsequent root tagged types declared in the declaration sequence, and specifies that no stream routines be generated. The form with an argument (for which there is also a corresponding aspect) specifies a single root tagged type for which stream routines are not to be generated.

Once the pragma has been given for a particular root tagged type, all subtypes and derived types of this type inherit the pragma automatically, so the effect applies to a complete hierarchy (this is necessary to deal with the class-wide dispatching versions of the stream routines).

When pragmas Discard_Names and No_Tagged_Streams are simultaneously applied to a tagged type its Expanded_Name and External_Tag are initialized with empty strings. This is useful to avoid exposing entity names at binary level but has a negative impact on the debuggability of tagged types.

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