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Stream class that provides copy-on-write functionality
Source position: resdatastream.pp line 61
type TResourceDataStream = class(TStream) |
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protected |
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function GetPosition; override; |
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procedure SetPosition(); override; |
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function GetSize; override; |
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procedure SetSize64(); override; |
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public |
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constructor Create(); |
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Creates a new object |
destructor Destroy; override; |
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function Compare(); |
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Compares the stream to another one |
procedure SetCustomStream(); |
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Sets a custom stream as the underlying stream |
function Read(); override; |
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function Write(); override; |
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function Seek(); override; |
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property Cached: Boolean; [rw] |
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Controls the copy-on-write behaviour of the stream |
end; |
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Stream class that provides copy-on-write functionality |
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This class provides the copy-on-write mechanism of TAbstractResource.RawData, via more levels of indirection.
It uses an underlying stream, to which it redirects operations.
The underlying stream can be a TCachedDataStream descendant, a memory stream or a custom stream. Usually when a resource is loaded from a stream, the underlying stream is a TCachedDataStream descendant, which provides a read-only stream-like interface over a portion of the original stream (that is, the part of the original stream where resource data resides). When TResourceDataStream is requested to write data, it replaces the underlying stream with a memory stream, whose contents are copied from the previous underlying stream: this way, copy-on-write functionality can be achieved.
As said before, third possibility is to have a custom stream as the underlying stream: a user can set this stream via TAbstractResource.SetCustomRawDataStream method, which in turn calls TResourceDataStream.SetCustomStream
Figure: Levels of indirection
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TResourceDataStream
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TMemoryStream TCachedDataStream descendant custom stream
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Base cached stream class |
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Creates a new object |
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Sets a custom stream as the underlying stream |