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Are there only 3 (4?) kinds?
----------------------------
* struct
* abstract struct <-- is this necessary
* concrete class with identity
* abstract class
Separate keywords or multiple "flag keywords"?
----------------------------------------------
Examples of keywords:
* value - value type
* identity - type with identity (always passed by reference)
* abstract - abstract/interface/trait
* concrete - concrete/leaf class
* mutable - has modifiable fields
Examples with flags on same line:
type value abstract Property of T
type identity abstract InputStream
type identity concrete createonly FileInputStream implements InputStream
Examples with flags on separate lines:
type Property of T
value
abstract
type InputStream
identity
abstract
type FileInputStream
implements InputStream
identity
concrete
createonly
Examples with flags on separate lines with prefix keyword:
type Property of T
typemode value
typemode abstract
type InputStream
typemode identity
typemode abstract
type FileInputStream
implements InputStream
typemode identity
typemode concrete
typemode createonly
Separate keywords examples:
| Abstract Concrete |
----------+---------------------------------+
Value | form record |
Identity | trait class |
----------+---------------------------------+
| Abstract Concrete |
----------+---------------------------------+
Value | form struct |
Identity | interface class |
----------+---------------------------------+
Or, have "identity" as a (built-in) interface:
class Point
class File implements Identity
Also, ref vs aliased vs embedded:
* maybe ref-ness could be decided by the compiler?
* aliased/non-aliased and linked/embedded, however, affect behavior.
Problems
--------
With this system, only leaf classes can be assumed to have / not have an
identity. So only leaf classes can be copied.
Maybe there's another way?
record = immutable unless concrete and "owned" and not aliased?
class = possibly mutable, can be aliased?
How to prevent mistakes
-----------------------
Incorrectly specifying a type as a value type can cause problems if
there's at least one mutable field
|
