abstract.sa


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-- $IS_EQ: Subtypes define "is_eq($OB):BOOL".
-- $IS_LT{T}: Subtypes define "is_lt(T):BOOL".
-- $HASH: Subtypes define "hash:INT".
-- $NIL: Subtypes define "nil:SAME".
-- $COPY: Subtypes define "copy:SAME"
-- $STR: Subtypes define "str:STR".
-- $ELT{T}: Subtypes define "elt!:T".


abstract class $IS_EQ

abstract class $IS_EQ is -- Subtypes of this define "is_eq:BOOL". Typically used in -- typecases to use instead of "=". Examples: INT < $IS_EQ, -- STR < $IS_EQ. -- NOTE: -- This equality should be an IMMUTABLE equality that is valid -- over the lifetime of the whole object. It should be possible -- to use this equality (and an associated hash value) to -- place an object in a hash table and then later retrieve it. is_eq(e:$OB):BOOL; -- True if self is equal arg for -- this element type. end;

abstract class $HASH < $IS_EQ

abstract class $HASH < $IS_EQ is -- Subtypes of this must provide a hash routine. This is the *new* -- $HASH class and is a subtype of $IS_EQ so that all subtypes must -- redefine both hash and is_eq. These two routines must work -- together - is_eq must refer to an immutable equality hash: INT; end;

abstract class $SUPPORTS_REHASH

abstract class $SUPPORTS_REHASH is -- A class that supports rehashing of its values, when its pointers -- have been changed (possibly mysteriously, such as by being restored -- from a string) rehash; end;

abstract class $IS_LT{T} < $IS_EQ

abstract class $IS_LT{T} < $IS_EQ is -- Subtypes of this define "is_lt(T):BOOL and is_eq($OB)". -- Typically used in typecases. -- Examples: INT < $IS_LT{INT}, STR < $IS_LT{INT}. -- -- Design Note: $IS_LT has the type parameter since objects are -- almost always comparable only with the same type. With the new -- rules, if is_lt were defined on e: $OB, then we would have to -- find some meaning for < with arbitrary objects. (you can't just -- return false - that makes >= be true!). -- Hence, objects will only define comparisons with themselves -- while the container classes can switch on $IS_LT{T} and then -- use the SYS::is_lt when the contained objects are not directly -- comparable is_lt(e:T):BOOL; -- True if self is less than arg for -- this element type. end;

abstract class $IS_NIL

abstract class $IS_NIL is -- Subtypes of this define "is_nil:BOOL". Typically used in typecases. -- Example: INT < $IS_NIL. is_nil:BOOL; -- Test whether a value is nil. -- This is necessary for types with unusual is_eq behavior (such -- as IEEE floats). end;

abstract class $NIL < $IS_NIL

abstract class $NIL < $IS_NIL is -- Inidicates that the subtype provides a nil value -- -- Designer's Note:The advantage of T over SAME is that in -- parametrized classes typecase e when $NILthen .... e.nil e.nil -- is now known to be of type T, whereas if it were SAME, you would -- need at least an extra level of typecase nil:SAME; end;

abstract class $COPY

abstract class $COPY is -- Indicates that a subtype provides a copy routine copy:SAME; -- Return a copy of self. end;

abstract class $STR

abstract class $STR is -- Subtypes of this define "str:STR". This should be a reasonable -- string representation of an object. str:STR; -- String form of self end;

abstract class $VAR

abstract class $VAR is -- Subtypes of this are reference classes that may be viewed -- as variables with a particular value. The value of the reference -- object is an object with value semantics as_value:$OB; -- Return the value of self end;

abstract class $ELT

abstract class $ELT is -- Subtypes will provide an elt! iterator that returns at least -- a $OB (it could be more specific). Most objects will actually -- subtype from $ELT{T} elt!: $OB; end;

abstract class $ELT{T} < $ELT

abstract class $ELT{T} < $ELT is -- Subtypes of this define "elt!:T". This is a stronger version of -- the generic $ELT routine elt!:T; -- Contained items. end;