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local x, y
local p1, p2 = 10, 20
DoSomething(x, y, function  callback() print(p1+ p2) end);

The callback will print your 30.

-----Original Message-----
From: Ando Sonenblick []
Sent: Friday, October 17, 2003 12:47 PM
To: Lua list
Subject: callback implementation details..


I have a feeling my question here is rather, well, stupid, but lua has
proven so amazingly flexible that I just may be surprised that what I'm
asking isn't just stupid, but actually possible....  yet I doubt it...

Anyway, I am about to implement callbacks...   so that a script can
call a C function to do some background process and when done, have the
C code execute a lua call back.  Here would be a standard way:

local x, y, p1, p2;
DoSomething(x, y, {function  callback(a, b) print(a+ b) end, p1, p2});

Where DoSomething is the call to C to initiate the bg process, x and y
are parameters for that process, and the table is the description of
the callback:

it has the function to execute and the (variable number) of parameters
to pass to it.

In this case, say p1 and p2 are 10 and 20 respectively, my C code
creates a ref to the table, does the work, then using the ref calls the
function callback, passing p1 and p2, which prints out 30.  I see no
problems with implementing this.

What I'd love (for simplification sake) would be to somehow already
pass the parameters to the function so that I don't have to have a
table, or do extra parsing/passing in my C code, etc.

So, in this case, things would look like (hypothetically speaking):

local x, y, p1, p2;
DoSomething(x, y, function callback(a = p1, b = p2) print(a+ b) end);  
    -- a is preassigned to p1 and b is preassigned to p2

so in this case (assuming 10 and 20 again for p1 and p2), my C code
could simply just call callback and the parameter a is already 10 and p
already 20, yielding the same print out of 30.

Is anything like this possible?


Ando Sonenblick
SpriTec Software