# multmeth.t | documentation

    #charset "us-ascii"

    /*
     *   Copyright (c) 2008 Michael J. Roberts.  All Rights Reserved.
     *
     *   This module provides the run-time component of "multi-methods" in TADS
     *   3.  This works with the compiler to implement a multiple-dispatch
     *   system.
     *
     *   Multi-methods are essentially a combination of regular object methods
     *   and "overloaded functions" in languages like C++.  Like a regular
     *   object method, multi-methods are polymorphic: you can define several
     *   incarnations of the same function name, with different parameter
     *   types, the system picks the right binding for each invocation
     *   dynamically, based on the actual argument values at run-time.  Unlike
     *   regular methods, though, the selection is made on ALL of the argument
     *   types, not just a special "self" argument.  In that respect,
     *   multi-methods are like overloaded functions in C++; but multi-methods
     *   differ from C++ overloading in that the selection of which method to
     *   call is made dynamically at run-time, not at compile time.
     *
     *   There are two main uses for multi-methods.
     *
     *   First, most obviously, multi-methods provide what's known as "multiple
     *   dispatch" semantics.  There are some situations (actually, quite a
     *   few) where the ordinary Object Oriented notion of polymorphism -
     *   selecting a method based on a single target object - doesn't quite do
     *   the trick, because what you really want to do is select a particular
     *   method based on the *combination* of objects involved in an operation.
     *   Some canonical examples are calculating intersections of shapes in a
     *   graphics program, where you want to select a specialized "Rectangle +
     *   Circle" routine in one case and a "Line + Polygon" routine in another;
     *   or performing file format conversions, where you want to select, say,
     *   a specialized "JPEG to PNG" routine.  In an IF context, the obvious
     *   use is for carrying out multi-object verbs, where you might want a
     *   special routine for PUT (liquid) IN (vessel), and another for PUT
     *   (object) IN (container).
     *
     *   Second, multi-methods offer a way of extending a class without having
     *   to change the class's source code.  Since a multi-method is defined
     *   externally to any classes it refers to, you can create a method that's
     *   polymorphic on class type - just like a regular method - but as a
     *   syntactically stand-alone function.  This feature isn't as important
     *   in TADS as in some other languages, since TADS lets you do essentially
     *   the same thing with the "modify" syntax; but for some purposes the
     *   multi-method approach might be preferable aesthetically, since it's
     *   wholly external to the class rather than a sort of lexically separate
     *   continuation of the class's code.  (However, as a practical matter,
     *   it's not all that different; our implementation of multi-methods does
     *   in fact modify the original class object, since we store the binding
     *   information in the class objects.)
     */

    #include <tads.h>

    /* ------------------------------------------------------------------------ */
    /*
     *   Invoke a multi-method function.  For an expression of the form
     *
     *.     f(a, b, ...)
     *
     *   where 'f' has been declared as a multi-method, the compiler will
     *   actually generate code that invokes this function, like so:
     *
     *.     _multiMethodCall(baseFunc, params);
     *
     *   'baseFunc' is a function pointer giving the base function; this is a
     *   pointer to the common stub function that the compiler generates to
     *   identify all of the multi-methods with a given name.  'params' is a
     *   list giving the actual parameter values for invoking the function.
     *
     *   Our job is to find the actual run-time binding for the function given
     *   the actual parameters, and invoke it.
     */
    _multiMethodCall(baseFunc, args)
    {
        /* get the function binding lookup information */
        local info = _multiMethodRegistry.boundFuncTab_[baseFunc];

        /* it's an error if there's no binding */
        if (info == nil)
            throw new UnboundMultiMethod(baseFunc, args);

        /*
         *   Look up the function binding based on the arguments.  To ensure
         *   that we match a function with the correct number of argument, we
         *   have to explicitly add the last-argument placeholder to the list.
         */
        local func = _multiMethodSelect(info, args + _multiMethodEndOfList);

        /* if we found a binding, invoke it; otherwise throw an error */
        if (func == nil)
            throw new UnboundMultiMethod(baseFunc, args);
        else
            return (func)(args...);
    }

    /*
     *   Invoke the base multi-method inherited from the given multi-method.
     *   'fromFunc' is a pointer to a multi-method, presumably the one
     *   currently running; we look up the next in line in inheritance order
     *   and invoke it with the given argument list.
     */
    _multiMethodCallInherited(fromFunc, [args])
    {
    #ifdef MULTMETH_STATIC_INHERITED

        /* static mode - get the cached inheritance information */
        local inh = _multiMethodRegistry.inhTab_[fromFunc];

    #else

        /* dynamic mode - get the base function binding */
        local info = _multiMethodRegistry.boundFuncTab_[
            _multiMethodRegistry.baseFuncTab_[fromFunc]];

        /* it's an error if it doesn't exist */
        if (info == nil)
            throw new UnboundInheritedMultiMethod(fromFunc, args);

        /* look up the inherited function based on the actual parameters */
        local inh = _multiMethodInherit(
            fromFunc, info, args + _multiMethodEndOfList);

    #endif

        /* it's an error if there's no inherited binding */
        if (inh == nil)
            throw new UnboundInheritedMultiMethod(fromFunc, args);

        /* call it */
        return (inh)(args...);
    }

    /* ------------------------------------------------------------------------ */
    /*
     *   Get a pointer to a resolved multi-method function.  This takes a
     *   pointer to the base function for the multi-method and a list of actual
     *   argument values, and returns a function pointer to the specific
     *   version of the multi-method that would be invoked if you called the
     *   multi-method with that argument list.
     *
     *   For example, if you want to get a pointer to the function that would
     *   be called if you were to call foo(x, y, z), you'd use:
     *
     *.     local func = getMultiMethodPointer(foo, x, y, z);
     *
     *   We return a pointer to the individual multi-method function that
     *   matches the argument list, or nil if there's no matching multi-method.
     */
    getMultiMethodPointer(baseFunc, [args])
    {
        /* get the function binding lookup information */
        local info = _multiMethodRegistry.boundFuncTab_[baseFunc];

        /* if there's no binding information, return failure */
        if (info == nil)
            return nil;

        /* look up and return the function binding based on the arguments */
        return _multiMethodSelect(info, args + _multiMethodEndOfList);
    }

    /* ------------------------------------------------------------------------ */
    /*
     *   Resolve a multi-method binding.  This function takes a binding
     *   property ID (the property we assign during the registration process to
     *   generate the binding tables) and a "remaining" argument list.  This
     *   function invokes itself recursively to traverse the arguments from
     *   left to right, so at each recursive invocation, we lop off the
     *   leftmost argument (the one we're working on currently) and pass in the
     *   remaining arguments in the list.
     *
     *   We look up the binding property on the first argument in the remaining
     *   argument list.  This can yield one of three things:
     *
     *   - The trivial result is nil, which means that this binding property
     *   has no definition on the first argument.  This doesn't necessarily
     *   mean that the whole function is undefined on the arguments; it only
     *   means that the current inheritance level we're looking at for the
     *   previous argument(s) has no binding.  If we get this result we simply
     *   return nil to tell the caller that it must look at an inherited
     *   binding for the previous argument.
     *
     *   - If the result is a function pointer, it's the bound function.  This
     *   is the final result for the recursion, so we simply return it.
     *
     *   - Otherwise, the result will be a new property ID, giving the property
     *   that resolves the binding for the *next* argument.  In this case, we
     *   use this property to resolve the next argument in the list by a
     *   recursive invocation.  If that recursive call succeeds (i.e., returns
     *   a non-nil value), we're done - we simply return the recursive result
     *   as though it were our own.  If it fails, it means that there's no
     *   binding for the particular subclass we're currently working on for the
     *   first argument - however, there could still be a binding for a parent
     *   class of the first argument.  So, we iterate up to any inherited
     *   binding for the first argument, and if we find one, we try again with
     *   the same recursive call.  We continue up our first argument's class
     *   tree until we either find a binding (in which case we return it) or
     *   exhaust the class tree (in which case we return nil).
     */
    _multiMethodSelect(prop, args)
    {
        local obj, binding;

        /*
         *   Get the first argument from the remaining arguments.  If it's not
         *   an object, use the placeholder object for non-object parameter
         *   bindings.
         */
        local orig = args[1];
        if (dataType(orig) not in (TypeObject, TypeList, TypeSString))
            orig = _multiMethodNonObjectBindings;

        /* get the remaining arguments */
        args = args.sublist(2);

        /*
         *   Look up the initial binding - this is simply the value of the
         *   binding property for the first argument.  In order to process the
         *   inheritance tree later, we'll need to know where we got this
         *   definition from, so look up the specific defining object.
         *
         *   If the initial binding property isn't defined, or its value is
         *   explicitly nil, the function isn't bound (or, in the case of nil,
         *   is explicitly unbound).  Inheritance won't help in these cases, so
         *   we can immediately return nil to indicate that we don't have a
         *   binding.
         */
        if ((obj = orig.propDefined(prop, PropDefGetClass)) == nil
            || (binding = obj.(prop)) == nil)
            return nil;

        /*
         *   If there are no more arguments, but we didn't just find a final
         *   function binding, we don't have enough arguments to match the
         *   current multi-method path.  Return failure.
         */
        if (args.length() == 0 && dataType(binding) != TypeFuncPtr)
            return nil;

        /*
         *   starting at our current defining object for the first argument,
         *   scan up its superclass tree until we find a binding
         */
        for (;;)
        {
            local ret;

            /* if we have a function pointer, we've found our binding */
            if (dataType(binding) == TypeFuncPtr)
                return binding;

            /*
             *   Recursively bind the binding for the remaining arguments.  If
             *   we find a binding, we're done - simply return it.
             */
            if ((ret = _multiMethodSelect(binding, args)) != nil)
                return ret;

            /*
             *   We didn't find a binding for the remaining arguments, so we
             *   must have chosen too specific a binding for the first
             *   argument.  Look for an inherited value of the binding property
             *   in the next superclass of the object where we found the last
             *   binding value.
             */
            obj = orig.propInherited(prop, orig, obj, PropDefGetClass);
            if (obj == nil)
                return nil;

            /* we found an inherited value, so retrieve it from the superclass */
            binding = obj.(prop);
        }
    }

    /*
     *   Select the INHERITED version of a multi-method.  This takes a
     *   particular version of the multi-method, and finds the next version in
     *   inheritance order.
     *
     *   This is basically a copy of _multiMethodSelect(), with a small amount
     *   of extra logic.  This code repetition isn't good maintenance-wise, and
     *   the two functions could in principle be merged into one.  However,
     *   doing so would have an efficiency cost to _multiMethodSelect(), which
     *   we want to keep as lean as possible.
     */
    _multiMethodInherit(fromFunc, prop, args)
    {
        return _multiMethodInheritMain(
            new _MultiMethodInheritCtx(), fromFunc, prop, args);
    }

    class _MultiMethodInheritCtx: object
        foundFromFunc = nil
    ;

    _multiMethodInheritMain(ctx, fromFunc, prop, args)
    {
        local obj, binding;

        /*
         *   Get the first argument from the remaining arguments.  If it's not
         *   an object, use the placeholder object for non-object parameter
         *   bindings.
         */
        local orig = args[1];
        if (dataType(orig) not in (TypeObject, TypeList, TypeSString))
            orig = _multiMethodNonObjectBindings;

        /* get the remaining arguments */
        args = args.sublist(2);

        /*
         *   Look up the initial binding - this is simply the value of the
         *   binding property for the first argument.  In order to process the
         *   inheritance tree later, we'll need to know where we got this
         *   definition from, so look up the specific defining object.
         *
         *   If the initial binding property isn't defined, or its value is
         *   explicitly nil, the function isn't bound (or, in the case of nil,
         *   is explicitly unbound).  Inheritance won't help in these cases, so
         *   we can immediately return nil to indicate that we don't have a
         *   binding.
         */
        if ((obj = orig.propDefined(prop, PropDefGetClass)) == nil
            || (binding = obj.(prop)) == nil)
            return nil;

        /*
         *   If there are no more arguments, but we didn't just find a final
         *   function binding, we don't have enough arguments to match the
         *   current multi-method path.  Return failure.
         */
        if (args.length() == 0 && dataType(binding) != TypeFuncPtr)
            return nil;

        /*
         *   starting at our current defining object for the first argument,
         *   scan up its superclass tree until we find a binding
         */
        for (;;)
        {
            /* we haven't found a function binding yet */
            local ret = nil;

            /*
             *   we either have a function pointer, in which case it's the
             *   actual binding, or a property, in which case it's the next
             *   binding level
             */
            if (dataType(binding) == TypeFuncPtr)
            {
                /* this is the binding */
                ret = binding;
            }
            else
            {
                /* if there are no more arguments, return failure */
                if (args.length() == 0)
                    return nil;

                /*
                 *   Recursively bind the binding for the remaining arguments.
                 *   If we find a binding, we're done - simply return it.
                 */
                ret = _multiMethodInheritMain(ctx, fromFunc, binding, args);
            }

            /* check to see if we found a binding */
            if (ret != nil)
            {
                /*
                 *   We found a binding.  If we've already found the inheriting
                 *   version, return the first thing we find, since that's the
                 *   next inheriting level.  Otherwise, if this is the
                 *   inheriting version, note that we've found it, but keep
                 *   looking, since we want to find the next one after that.
                 *   Otherwise, just keep looking, since we haven't even
                 *   reached the overriding version yet.
                 */
                if (ctx.foundFromFunc)
                    return ret;
                else if (ret == fromFunc)
                    ctx.foundFromFunc = true;
            }

            /*
             *   We didn't find a binding for the remaining arguments, so we
             *   must have chosen too specific a binding for the first
             *   argument.  Look for an inherited value of the binding property
             *   in the next superclass of the object where we found the last
             *   binding value.
             */
            obj = orig.propInherited(prop, orig, obj, PropDefGetClass);
            if (obj == nil)
                return nil;

            /* we found an inherited value, so retrieve it from the superclass */
            binding = obj.(prop);
        }
    }

    /* ------------------------------------------------------------------------ */
    /*
     *   Unbound multi-method exception.  This is thrown when a call to resolve
     *   a multi-method fails to find a binding, meaning that there's no
     *   definition of the method that matches the types of the arguments.
     */
    class UnboundMultiMethod: Exception
        construct(func, args)
        {
            /* note the function name and argument list */
            func_ = func;
            args_ = args;

            /* look up the function's name */
            name_ = _multiMethodRegistry.funcNameTab_[func];
        }

        /* display an error message describing the exception */
        displayException()
        {
            "Unbound multi-method \"<<name_>>\" (<<args_.length()>> argument(s))";
        }

        /* the base function pointer */
        func_ = nil

        /* the symbol name of the base function */
        name_ = ''

        /* the number of arguments */
        args_ = 0
    ;

    class UnboundInheritedMultiMethod: UnboundMultiMethod
        displayException()
        {
            "No inherited multi-method for \"<<name_>>\" (<<args_.length()>>
            arguments(s))";
        }
    ;

    /* ------------------------------------------------------------------------ */
    /*
     *   Base class for our internal placeholder objects for argument list
     *   matching.
     */
    class _MultiMethodPlaceholder: object
    ;

    /*
     *   A placeholder object for bindings for non-object arguments.  Whenever
     *   we have an actual argument value that's not an object, we'll look here
     *   for bindings for that parameter.  When registering a function, we'll
     *   register a binding here for any parameter that doesn't have a type
     *   specification.
     */
    _multiMethodNonObjectBindings: _MultiMethodPlaceholder
    ;

    /*
     *   A placeholder object for end-of-list bindings.  When we're matching an
     *   argument list, we'll use this to represent the end of the list so that
     *   we can match the "..." in any varargs functions in the multi-method
     *   set that we're matching against.
     */
    _multiMethodEndOfList: _MultiMethodPlaceholder
    ;

    /* ------------------------------------------------------------------------ */
    /*
     *   Register a multi-method.
     *
     *   The compiler automatically generates a call to this function during
     *   pre-initialization for each defined multi-method.  'baseFunc' is a
     *   pointer to the "base" function - this is a stub function that the
     *   compiler generates to refer to the whole collection of multi-methods
     *   with a given name.  'func' is the pointer to the specific multi-method
     *   we're registering; this is the actual function defined in the code
     *   with a given set of parameter types.  'params' is a list of the
     *   parameter type values; each parameter type in the list is given as a
     *   class object (meaning that the parameter matches that class), nil
     *   (meaning that the parameter matches ANY type of value), or the string
     *   '...' (meaning that this is a "varargs" function, and any number of
     *   additional parameters can be supplied at this point in the parameters;
     *   this is always the last parameter in the list if it's present).
     */
    _multiMethodRegister(baseFunc, func, params)
    {
        /* if there's no hash entry for the function yet, add one */
        local tab = _multiMethodRegistry.funcTab_;
        if (tab[baseFunc] == nil)
            tab[baseFunc] = new Vector(10);

        /* add the entry to the list of variants for this function */
        tab[baseFunc].append([func, params]);

        /* add the mapping from the function to the base function */
        _multiMethodRegistry.baseFuncTab_[func] = baseFunc;

        /* also add the function to the direct parameter table */
        _multiMethodRegistry.funcParamTab_[func] = params;
    }

    /*
     *   Build the method bindings.  The compiler generates a call to this
     *   after all methods have been registered; we run through the list of
     *   registered methods and generate the binding properties in the
     *   referenced objects.
     */
    _multiMethodBuildBindings()
    {
        /* no errors yet */
        local errs = [];

        /*
         *   build a lookup table that maps function pointers to symbol names,
         *   so we can look up our function names for diagnostic purposes
         */
        local nameTab = new LookupTable(128, 256);
        t3GetGlobalSymbols().forEachAssoc(function(key, val)
        {
            /* if it's a function, store a value-to-name association */
            if (dataType(val) == TypeFuncPtr)
                nameTab[val] = key;
        });

        /* run through each entry in the method table */
        _multiMethodRegistry.funcTab_.forEachAssoc(function(baseFunc, val)
        {
            /* look up the base function's name */
            local name = nameTab[baseFunc];

            /* add this to the saved name table */
            _multiMethodRegistry.funcNameTab_[baseFunc] = name;

            /* note the number of registered instances of this function */
            local funcCnt = val.length();

            /*
             *   Assign the initial binding property for this function.  This
             *   is the property that gives us the binding for the first
             *   variant argument.  Each unique multi-method (which is defined
             *   as a multi-method with a given name and a given number of
             *   parameters) has a single initial binding property.
             */
            local initProp = t3AllocProp();

            /*
             *   store the binding starter information for the function - to
             *   find the binding on invocation, we'll need the initial binding
             *   property so that we can trace the argument list
             */
            _multiMethodRegistry.boundFuncTab_[baseFunc] = initProp;

            /* build the argument binding tables */
            for (local i = 1 ; i <= funcCnt ; i++)
            {
                /* get the function binding */
                local func = val[i][1];

                /* get the formal parameter type list for this function */
                local params = val[i][2];
                local paramCnt = params.length();

                /*
                 *   If the last formal isn't a varargs placeholder, then we
                 *   must explicitly find the end of the list in the actual
                 *   parameters in order to match a call.  To match the end of
                 *   the list, add the special End-Of-List placeholder to the
                 *   formals list.
                 *
                 *   This isn't necessary when there's a varargs placeholder
                 *   because the placeholder can match zero or more - so it
                 *   doesn't matter where the list ends as long as we get to
                 *   the varargs slot.
                 */
                if (paramCnt == 0 || params[paramCnt] != '...')
                {
                    params += _multiMethodEndOfList;
                    ++paramCnt;
                }

                /* start at the initial binding property */
                local prop = initProp;

                /* run through the parameters and build the bindings */
                for (local j = 1 ; j <= paramCnt ; j++)
                {
                    /* get this parameter type */
                    local origTyp = params[j], typ = origTyp;

                    /*
                     *   If the type is nil, it means that this parameter slot
                     *   can accept any type.  So, map the slot to the generic
                     *   Object type - this will catch everything, since we
                     *   handle non-objects by mapping them to the
                     *   _multiMethodNonObjectBindings placeholder object,
                     *   which like all objects inherits from Object.  This
                     *   means we'll match argument values that are objects or
                     *   non-objects, thus fulfilling our requirement to match
                     *   all values.
                     *
                     *   If the type is the string '...', it means that this is
                     *   a varargs placeholder argument.  In this case, we need
                     *   to set up a match for the generic Object, in case we
                     *   have one or more actual arguments for the varargs
                     *   portion.  This will also automatically match the case
                     *   where we have no extra arguments, because in this case
                     *   the matcher will try to match the End-Of-List
                     *   placeholder object _multiMethodEndOfList, which (as
                     *   above) inherits from Object and thus picks up the
                     *   any-type binding.
                     *
                     *   The one tricky bit is that when we have a parameter
                     *   explicitly bound to Object, or an explicit End-Of-List
                     *   flag object, we'll get an undesired side effect of
                     *   this otherwise convenient arrangement: we'll
                     *   effectively bind non-object types to the Object by
                     *   virtue of the inheritance.  To deal with this, we'll
                     *   explicitly set the placeholders' binding to nil in
                     *   this situation - this makes non-object types
                     *   explicitly *not* bound to the function, overriding any
                     *   binding we'd otherwise inherit from Object.
                     */
                    if (typ == nil || typ == '...')
                        typ = Object;

                    /*
                     *   Figure the binding.
                     *
                     *   - If this is the last parameter, it's the end of the
                     *   line, so bind directly to the function pointer.
                     *
                     *   - If this isn't the variant parameter, the binding is
                     *   the next binding property.  At invocation, we'll
                     *   continue on to the next argument value, evaluating
                     *   this next property to get its binding in the context
                     *   established by the current argument and property.  The
                     *   next binding property is specific to the current class
                     *   in the current position, so we might already have
                     *   assigned a property for it from another version of
                     *   this function.  Look it up, or create a new one if we
                     *   haven't assigned it already.
                     */
                    local binding;
                    if (j == paramCnt)
                    {
                        /* end of the line - the binding is the actual function */
                        binding = func;

                        /*
                         *   if this type is already bound to a different
                         *   definition for this function, we have a
                         *   conflicting definition
                         */
                        if (typ.propDefined(prop, PropDefDirectly)
                            && typ.(prop) != binding)
                            errs += [baseFunc, func, params, name];
                    }
                    else
                    {
                        /* check for an existing binding property here */
                        if (typ.propDefined(prop, PropDefDirectly))
                        {
                            /* we already have a forward binding here - use it */
                            binding = typ.(prop);
                        }
                        else
                        {
                            /* it's not defined here, so create a new property */
                            binding = t3AllocProp();
                        }
                    }

                    /* set the binding */
                    typ.(prop) = binding;

                    /*
                     *   As we mentioned above, if the original type is
                     *   explicitly Object, we *don't* want to allow non-object
                     *   types (int, true, nil, property pointers, etc) and
                     *   End-Of-List placeholders to match - without some kind
                     *   of explicit intervention here, the placeholders would
                     *   match by inheritance because the placeholders are just
                     *   objects themselves.  To handle this properly, set the
                     *   non-object placeholder bindings explicitly to nil.
                     */
                    if (origTyp == Object)
                        _MultiMethodPlaceholder.(prop) = nil;

                    /*
                     *   if there's another argument, this binding is the
                     *   binding property for the next argument
                     */
                    prop = binding;
                }
            }
        });

    #ifdef MULTMETH_STATIC_INHERITED
        /*
         *   If we're operating in static inheritance mode, cache the
         *   next-override information for inherited() calls.  Since we're
         *   using static inheritance, we can figure this at startup and just
         *   look up the cached information whenever we need to perform an
         *   inherited() call.
         */
        _multiMethodRegistry.funcTab_.forEachAssoc(function(baseFunc, val)
        {
            /* get the binding property for the base function */
            local prop = _multiMethodRegistry.boundFuncTab_[baseFunc];

            /* run through the functions registered under this function name */
            for (local i = 1 ; i <= val.length() ; i++)
            {
                /* get this function binding and the type list */
                local func = val[i][1];
                local params = val[i][2];
                local paramCnt = params.length();

                /*
                 *   Add the end-of-list marker if applicable.  For a varargs
                 *   function, add one generic Object parameter in place of the
                 *   variable list - but we'll check later to make sure that
                 *   any match we find is really varargs, since a varargs
                 *   function can only inherit from another varargs function.
                 *   (This is because, in order to actually invoke the
                 *   inherited function from an overrider, the callee must be
                 *   varargs to be able to handle varargs from the caller.)
                 */
                local varargs = (paramCnt != 0 && params[paramCnt] == '...');
                if (varargs)
                    params[paramCnt] = Object;
                else
                    params += _multiMethodEndOfList;

                /* look up the inherited version of the method */
                local inh = _multiMethodInherit(func, prop, params);

                /* varargs can only inherit from varargs */
                if (inh != nil && varargs)
                {
                    /* look up the inherited parameters */
                    local inhParams = _multiMethodRegistry.funcParamTab_[inh];
                    local inhParamCnt = inhParams.length();

                    /* make sure it's varargs, too */
                    if (inhParamCnt == 0 || inhParams[inhParamCnt] != '...')
                        inh = nil;
                }

                /* remember the inherited function */
                _multiMethodRegistry.inhTab_[func] = inh;
            }
        });
    #endif /* MULTMETH_STATIC_INHERITED */

        /* we're done with the source bindings - discard them to save memory */
        _multiMethodRegistry.funcTab_ = nil;
        _multiMethodRegistry.funcParamTab_ = nil;
    }

    /*
     *   Multi-method registry.  This is where we keep the registry information
     *   that we build during initialization.
     */
    _multiMethodRegistry: object
        /* table of registered functions, indexed by base function */
        funcTab_ = static new LookupTable(128, 256)

        /* table of function parameter lists, indexed by function */
        funcParamTab_ = static new LookupTable(128, 256)

        /* function name table */
        funcNameTab_ = static new LookupTable(64, 128)

        /* base function -> initial binding property */
        boundFuncTab_ = static new LookupTable(64, 128)

        /* function -> base function */
        baseFuncTab_ = static new LookupTable(64, 128)

    #ifdef MULTMETH_STATIC_INHERITED
        /* table of cached inherited() information, indexed by function */
        inhTab_ = static new LookupTable(64, 128)
    #endif
    ;

Adv3Lite Library Reference Manual
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