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The abstract type Root_Stream_Type is the root type of the class of
stream types. The types in this class represent different kinds of
streams. A new stream type is defined by extending the root type (or
some other stream type), overriding the Read and Write operations, and
optionally defining additional primitive subprograms, according to the
requirements of the particular kind of stream. The predefined
stream-oriented attributes like T'Read and T'Write make dispatching
calls on the Read and Write procedures of the Root_Stream_Type.
(User-defined T'Read and T'Write attributes can also make such calls, or
can call the Read and Write attributes of other types.)
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package Ada.Streams is
pragma Pure(Streams);
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type Root_Stream_Type is abstract tagged limited private;
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type Stream_Element is mod implementation-defined;
type Stream_Element_Offset is range implementation-defined;
subtype Stream_Element_Count is
Stream_Element_Offset range 0..Stream_Element_Offset'Last;
type Stream_Element_Array is
array(Stream_Element_Offset range <>) of Stream_Element;
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procedure Read(
Stream : in out Root_Stream_Type;
Item : out Stream_Element_Array;
Last : out Stream_Element_Offset) is abstract;
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procedure Write(
Stream : in out Root_Stream_Type;
Item : in Stream_Element_Array) is abstract;
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private
... -- not specified by the language
end Ada.Streams;
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The Read operation transfers Item'Length stream elements from the
specified stream to fill the array Item. The index of the last stream
element transferred is returned in Last. Last is less than Item'Last
only if the end of the stream is reached.
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The Write operation appends Item to the specified stream.
NOTES
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(30) See section A.12.1 The Package Streams.Stream_IO, for an example of
extending type Root_Stream_Type.