Encoding Snips

The generalized notion of a snip allows new snip types to be defined and immediately used in any editor class. Also, when two applications support the same kinds of snips, snip data can easily be cut and pasted between them, and the same data files will be readable by each program. This interoperability is due to a consistent encoding mechanism that is built into the snip system.

Graceful and extensible encoding of snips requires that two issues are addressed:

• In order to convert a snip from an encoded representation (e.g., as bytes in a file) to a memory object, a decoding function must be provided for each type of snip. Furthermore, a list of such decoders must be available to the high-level decoding process. This decoding mapping is defined by associating a snip class object to every snip. A snip class is an instance of the snip-class% class.
• Some editors may require additional information to be stored about a snip; this information is orthogonal to the type-specific information stored by the snip itself. For example, a pasteboard needs to remember a snip's position, while a text editor does not need this information. If data is being cut and pasted from one pasteboard to another, then information about relative positions needs to be maintained, but this information should not inhibit pasting into an editor. Extra data is associated with a snip through editor data objects, instances of the editor-data% class; decoding requires that each editor data object has a editor data class, an instance of the editor-data-class% class.

Snip classes, snip data, and snip data classes solve problems related to encoding and decoding snips. In an application that has no need for saving files or cut-and-paste, these issues can be safely ignored.

• Snip Classes
• Editor Data