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- Subject: OP_SELF (was Re: Application of indexing to all types)
- From: Mark Hamburg <mhamburg@...>
- Date: Fri, 25 Feb 2005 09:45:30 -0800
The piece of code of real interest is the code in lvm.c that implements
OP_SELF. Essentially what the language gives you at that point is a target
value and a string. OP_SELF needs to come up with a callable entity (e.g., a
function) and a target.
The existing implementation for OP_SELF is effectively:
function OP_SELF( obj, msg )
return obj[ msg ], obj
Examples of alternative implementations would include the __methods
metatable patch which provides a metatable entry akin to __index but
accessed only by the colon operator.
function metafield( t, k )
local mt = getmetatable( t )
return mt and rawget( mt, k )
function lookup( handler, t, k )
if handler == nil then
elseif type( handler ) == "table" then
return handler[ k ]
return handler( t, k )
function OP_SELF_methods( obj, msg )
local f = rawget( obj, msg )
if f == nil then
f = lookup( metafield( obj, "__methods" ), obj, msg )
if f == nil then
f = lookup( metafield( obj, "__index" ), obj, msg )
return f, msg
If one redefines OP_SELF, then there probably need to be the following
additional enhancements since the necessary information may not be readily
lua_getmethod( lua_State* L ): A C API extension that takes the top two
objects on the stack as obj and msg and does the appropriate method lookup.
bindmethod( obj, msg ): A Lua function that takes an object and a message
and returns a closure that sends msg to obj with any other parameters passed
to the closure.
hasmethod( obj, msg ): A Lua function that tests for the presence of a
message -- i.e., it tells you whether it would be safe to send the message.