Cleanup Issue COMMON-TYPE
- Status
- Passed, Mar 89 X3J13
- Category
- CHANGE
- References
- CLtL p.35, p.76
Problem Description
The type COMMON is defined in a very peculiar way and does not seem to be useful for anything. It can be extended by users using DEFSTRUCT, but not DEFTYPE nor DEFCLASS, but it cannot be extended by implementations. Whether certain types such as NUMBER and ARRAY are subtypes of COMMON is implementation-dependent. The goal of having the COMMON type was probably to improve portability, but it is unclear how it could actually be used in that way.Proposal (REMOVE)
Remove COMMON and COMMONP from the language.Rationale
Keeping the definition of COMMON accurate in the new specification, in the face of changes elsewhere in the language such as the introduction of CLOS and the possible introduction of character registries, is difficult when no one is sure what COMMON is for. If no one uses COMMON, it would be less work to just get rid of it.Current Practice
Every implementation probably implements COMMON. Moon has never seen it used except in a program to test whether its implementation matched CLtL.Cost to Implementors
None.Cost to Users
None unless they are actually using COMMON.Cost of Non-Adoption
Implementors would have to maintain COMMON. Users would have to try to understand it, or figure out that they didn't care about it.
None.Benefits
Simpler language.Aesthetics
Simpler language.Discussion
None.Edit History
- Version 1, 20-Mar-89, by Moon