ficl/softwords/oo.fr

\ ** ficl/softwords/oo.fr
\ ** F I C L   O - O   E X T E N S I O N S
\ ** john sadler aug 1998
\
\ $FreeBSD: head/sys/boot/ficl/softwords/oo.fr 60959 2000-05-26 21:35:08Z dcs $


.( loading ficl O-O extensions ) cr
7 ficl-vocabulary oop
also oop definitions

\ Design goals:
\ 0. Traditional OOP: late binding by default for safety.
\    Early binding if you ask for it.
\ 1. Single inheritance
\ 2. Object aggregation (has-a relationship)
\ 3. Support objects in the dictionary and as proxies for
\    existing structures (by reference):
\    *** A ficl object can wrap a C struct ***
\ 4. Separate name-spaces for methods - methods are
\    only visible in the context of a class / object
\ 5. Methods can be overridden, and subclasses can add methods.
\    No limit on number of methods.

\ General info:
\ Classes are objects, too: all classes are instances of METACLASS
\ All classes are derived (by convention) from OBJECT. This
\ base class provides a default initializer and superclass
\ access method

\ A ficl object binds instance storage (payload) to a class.
\ object  ( -- instance class )
\ All objects push their payload address and class address when
\ executed. All objects have this footprint:
\ cell 0: first payload cell

\ A ficl class consists of a parent class pointer, a wordlist
\ ID for the methods of the class, and a size for the payload
\ of objects created by the class. A class is an object.
\ The NEW method creates and initializes an instance of a class.
\ Classes have this footprint:
\ cell 0: parent class address
\ cell 1: wordlist ID
\ cell 2: size of instance's payload

\ Methods expect an object couple ( instance class )
\ on the stack.
\ Overridden methods must maintain the same stack signature as
\ their predecessors. Ficl has no way of enforcing this, though.

user current-class
0 current-class !

\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ ** L A T E   B I N D I N G
\ Compile the method name, and code to find and
\ execute it at run-time...
\ parse-method compiles the method name so that it pushes
\ the string base address and count at run-time.
\
: parse-method  \ name  run: ( -- c-addr u )
    parse-word
	postpone sliteral
; compile-only

: lookup-method  ( class c-addr u -- class xt )
	2dup
	local u
	local c-addr
	end-locals
	2 pick cell+ @		( -- class c-addr u wid )
	search-wordlist 	( -- class 0 | xt 1 | xt -1 )
	0= if
		c-addr u type ."  not found in "
        body> >name type
        cr abort
	endif
;

: exec-method  ( instance class c-addr u -- <method-signature> )
    lookup-method execute
;

: find-method-xt   \ name ( class -- class xt )
	parse-word lookup-method
;


\ Method lookup operator takes a class-addr and instance-addr
\ and executes the method from the class's wordlist if
\ interpreting. If compiling, bind late.
\
: -->   ( instance class -- ??? )
    state @ 0= if
		find-method-xt execute
    else
		parse-method  postpone exec-method
    endif
; immediate


\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ ** E A R L Y   B I N D I N G
\ Early binding operator compiles code to execute a method
\ given its class at compile time. Classes are immediate,
\ so they leave their cell-pair on the stack when compiling.
\ Example:
\   : get-wid   metaclass => .wid @ ;
\ Usage
\   my-class get-wid  ( -- wid-of-my-class )
\
: =>   \ c:( class meta -- ) run: ( -- ??? ) invokes compiled method
	drop find-method-xt compile, drop
; immediate compile-only


\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ ** I N S T A N C E   V A R I A B L E S
\ Instance variables (IV) are represented by words in the class's
\ private wordlist. Each IV word contains the offset
\ of the IV it represents, and runs code to add that offset
\ to the base address of an instance when executed.
\ The metaclass SUB method, defined below, leaves the address
\ of the new class's offset field and its initial size on the
\ stack for these words to update. When a class definition is
\ complete, END-CLASS saves the final size in the class's size
\ field, and restores the search order and compile wordlist to
\ prior state. Note that these words are hidden in their own
\ wordlist to prevent accidental use outside a SUB END-CLASS pair.
\
wordlist
dup constant instance-vars
dup >search ficl-set-current
: do-instance-var
    does>   ( instance class addr[offset] -- addr[field] )
		nip @ +
;

: addr-units:  ( offset size "name" -- offset' )
    create over , +
    do-instance-var
;

: chars:	\ ( offset nCells "name" -- offset' ) Create n char member.
   chars addr-units: ;

: char:		\ ( offset nCells "name" -- offset' ) Create 1 char member.
   1 chars: ;

: cells:  ( offset nCells "name" -- offset' )
	cells >r aligned r> addr-units:
;

: cell:   ( offset nCells "name" -- offset' )
    1 cells: ;

\ Aggregate an object into the class...
\ Needs the class of the instance to create
\ Example: object obj: m_obj
\
: do-aggregate
	does>   ( instance class pfa -- a-instance a-class )
	2@          ( inst class a-class a-offset )
	2swap drop  ( a-class a-offset inst )
	+ swap		( a-inst a-class )
;

: obj:   ( offset class meta "name" -- offset' )
    locals| meta class offset |
    create  offset , class ,
	class meta --> get-size  offset +
	do-aggregate
;

\ Aggregate an array of objects into a class
\ Usage example:
\ 3 my-class array: my-array
\ Makes an instance variable array of 3 instances of my-class
\ named my-array.
\
: array:   ( offset n class meta "name" -- offset' )
	locals| meta class nobjs offset |
	create offset , class ,
	class meta --> get-size  nobjs * offset +
	do-aggregate
;

\ Aggregate a pointer to an object: REF is a member variable
\ whose class is set at compile time. This is useful for wrapping
\ data structures in C, where there is only a pointer and the type
\ it refers to is known. If you want polymorphism, see c_ref
\ in classes.fr. REF is only useful for pre-initialized structures,
\ since there's no supported way to set one.
: ref:   ( offset class meta "name" -- offset' )
	locals| meta class offset |
	create offset , class ,
	offset cell+
	does>    ( inst class pfa -- ptr-inst ptr-class )
	2@       ( inst class ptr-class ptr-offset )
	2swap drop + @ swap
;

\ END-CLASS terminates construction of a class by storing
\  the size of its instance variables in the class's size field
\ ( -- old-wid addr[size] 0 )
\
: end-class  ( old-wid addr[size] size -- )
    swap ! set-current
	search> drop		\ pop struct builder wordlist
;

set-current previous
\ E N D   I N S T A N C E   V A R I A B L E S


\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ D O - D O - I N S T A N C E
\ Makes a class method that contains the code for an
\ instance of the class. This word gets compiled into
\ the wordlist of every class by the SUB method.
\ PRECONDITION: current-class contains the class address
\ why use a state variable instead of the stack?
\ >> Stack state is not well-defined during compilation	(there are
\ >> control structure match codes on the stack, of undefined size
\ >> easiest way around this is use of this thread-local variable
\
: do-do-instance  ( -- )
    s" : .do-instance does> [ current-class @ ] literal ;"
    evaluate
;

\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ ** M E T A C L A S S
\ Every class is an instance of metaclass. This lets
\ classes have methods that are different from those
\ of their instances.
\ Classes are IMMEDIATE to make early binding simpler
\ See above...
\
:noname
	wordlist
	create
    immediate
	0       ,	\ NULL parent class
	dup     ,	\ wid
	3 cells ,	\ instance size
	ficl-set-current
	does> dup
;  execute metaclass

metaclass drop current-class !
do-do-instance

\
\ C L A S S   M E T H O D S
\
instance-vars >search

create .super  ( class metaclass -- parent-class )
    0 cells , do-instance-var

create .wid    ( class metaclass -- wid ) \ return wid of class
    1 cells , do-instance-var

create  .size  ( class metaclass -- size ) \ return class's payload size
    2 cells , do-instance-var

previous

: get-size    metaclass => .size  @ ;
: get-wid     metaclass => .wid   @ ;
: get-super   metaclass => .super @ ;

\ create an uninitialized instance of a class, leaving
\ the address of the new instance and its class
\
: instance   ( class metaclass "name" -- instance class )
    locals| meta parent |
	create
    here parent --> .do-instance \ ( inst class )
    parent meta metaclass => get-size
    allot                        \ allocate payload space
;

\ create an uninitialized array
: array   ( n class metaclass "name" -- n instance class )
    locals| meta parent nobj |
	create  nobj
    here parent --> .do-instance \ ( nobj inst class )
    parent meta metaclass => get-size
	nobj *  allot			\ allocate payload space
;

\ create an initialized instance
\
: new   \ ( class metaclass "name" -- )
    metaclass => instance --> init
;

\ create an initialized array of instances
: new-array   ( n class metaclass "name" -- )
	metaclass => array
	--> array-init
;

\ Create an anonymous initialized instance from the heap
: alloc   \ ( class metaclass -- instance class )
    locals| meta class |
    class meta metaclass => get-size allocate   ( -- addr fail-flag )
    abort" allocate failed "                    ( -- addr )
    class 2dup --> init
;

\ Create an anonymous array of initialized instances from the heap
: alloc-array   \ ( n class metaclass -- instance class )
    locals| meta class nobj |
    class meta metaclass => get-size
    nobj * allocate                 ( -- addr fail-flag )
    abort" allocate failed "        ( -- addr )
    nobj over class --> array-init
    class
;

\ create a proxy object with initialized payload address given
: ref   ( instance-addr class metaclass "name" -- )
    drop create , ,
    does> 2@
;

\ create a subclass
: sub   ( class metaclass "name" -- old-wid addr[size] size )
    wordlist
	locals| wid meta parent |
	parent meta metaclass => get-wid
	wid wid-set-super
	create  immediate
	here current-class !	\ prep for do-do-instance
	parent ,	\ save parent class
	wid    ,	\ save wid
	here parent meta --> get-size dup ,  ( addr[size] size )
	metaclass => .do-instance
	wid ficl-set-current -rot
	do-do-instance
	instance-vars >search	\ push struct builder wordlist
;

\ OFFSET-OF returns the offset of an instance variable
\ from the instance base address. If the next token is not
\ the name of in instance variable method, you get garbage
\ results -- there is no way at present to check for this error.
: offset-of   ( class metaclass "name" -- offset )
    drop find-method-xt nip >body @ ;

\ ID returns the string name cell-pair of its class
: id   ( class metaclass -- c-addr u )
	drop body> >name  ;

\ list methods of the class
: methods \ ( class meta -- )
	locals| meta class |
	begin
		class body> >name type ."  methods:" cr
		class meta --> get-wid >search words cr previous
		class meta metaclass => get-super
		dup to class
	0= until  cr
;

\ list class's ancestors
: pedigree  ( class meta -- )
	locals| meta class |
	begin
		class body> >name type space
		class meta metaclass => get-super
		dup to class
	0= until  cr
;

\ decompile a method
: see  ( class meta -- )
    metaclass => get-wid >search see previous ;

set-current
\ E N D   M E T A C L A S S

\ META is a nickname for the address of METACLASS...
metaclass drop
constant meta

\ SUBCLASS is a nickname for a class's SUB method...
\ Subclass compilation ends when you invoke end-class
\ This method is late bound for safety...
: subclass   --> sub ;


\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ ** O B J E C T
\ Root of all classes
:noname
	wordlist
	create  immediate
	0       ,	\ NULL parent class
	dup     ,	\ wid
	0       ,	\ instance size
	ficl-set-current
	does> meta
;  execute object

object drop current-class !
do-do-instance

\ O B J E C T   M E T H O D S
\ Convert instance cell-pair to class cell-pair
\ Useful for binding class methods from an instance
: class  ( instance class -- class metaclass )
	nip meta ;

\ default INIT method zero fills an instance
: init   ( instance class -- )
    meta
    metaclass => get-size   ( inst size )
    erase ;

\ Apply INIT to an array of NOBJ objects...
\
: array-init   ( nobj inst class -- )
	0 dup locals| &init &next class inst |
	\
	\ bind methods outside the loop to save time
	\
	class s" init" lookup-method to &init
	      s" next" lookup-method to &next
	drop
	0 ?do
		inst class 2dup
		&init execute
		&next execute  drop to inst
	loop
;

\ free storage allocated to a heap instance by alloc or alloc-array
\ NOTE: not protected against errors like FREEing something that's
\ really in the dictionary.
: free   \ ( instance class -- )
	drop free
	abort" free failed "
;

\ Instance aliases for common class methods
\ Upcast to parent class
: super     ( instance class -- instance parent-class )
    meta  metaclass => get-super ;

: pedigree  ( instance class -- )
	object => class
    metaclass => pedigree ;

: size      ( instance class -- sizeof-instance )
	object => class
    metaclass => get-size ;

: methods   ( instance class -- )
	object => class
    metaclass => methods ;

\ Array indexing methods...
\ Usage examples:
\ 10 object-array --> index
\ obj --> next
\
: index   ( n instance class -- instance[n] class )
	locals| class inst |
	inst class
    object => class
	metaclass => get-size  *   ( n*size )
	inst +  class ;

: next   ( instance[n] class -- instance[n+1] class )
	locals| class inst |
	inst class
    object => class
	metaclass => get-size
	inst +
	class ;

: prev   ( instance[n] class -- instance[n-1] class )
	locals| class inst |
	inst class
    object => class
	metaclass => get-size
	inst swap -
	class ;

set-current
\ E N D   O B J E C T


previous definitions