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Graham Wakefield wrote:

_G["print"]("hello to you too")

On Dec 12, 2006, at 12:46 AM, Austin Xu Wang wrote:


$ lua
Lua 5.1.1  Copyright (C) 1994-2006 Lua.org, PUC-Rio

array={print}
array[1]("Hello World!")

Hello World!
I think the question was not "how to call a function indirectly", but "how to call the n-th function of the, say, iolib array?" 

The answer is: you can't.  Not in the Lua side, at least.
If you want to optimize your code, make the function local - Lua will use a local by it's index, avoiding a table lookup. 

Example:

local print = print -- or '_G.print' or 'mypackage.print'

function main()
    print("hello wolrd");
end -- "end function" ?

main()


Inspecting the output of luac -l, you will see:

> cat > test.lua
function main()
    print("hello world")
end

> luac50 -l test.lua

main <test.lua:0> (3 instructions, 12 bytes at 00325910)
0 params, 2 stacks, 0 upvalues, 0 locals, 1 constant, 1 function
        1       [3]     CLOSURE         0 0     ; 00325A70
        2       [1]     SETGLOBAL       0 0     ; main
        3       [3]     RETURN          0 1 0

function <test.lua:1> (4 instructions, 16 bytes at 00325A70)
0 params, 2 stacks, 0 upvalues, 0 locals, 2 constants, 0 functions
        1       [2]     GETGLOBAL       0 0     ; print
        2       [2]     LOADK           1 1     ; "hello world"
        3       [2]     CALL            0 2 1
        4       [3]     RETURN          0 1 0


And the version with locals:

> cat > test-local.lua
local print = print
function main()
    print("hello world")
end

> luac50 -l test-local.lua

main <test-local.lua:0> (5 instructions, 20 bytes at 00325918)
0 params, 2 stacks, 0 upvalues, 1 local, 2 constants, 1 function
        1       [1]     GETGLOBAL       0 0     ; print
        2       [4]     CLOSURE         1 0     ; 00325BA8
        3       [4]     MOVE            0 0 0
        4       [2]     SETGLOBAL       1 1     ; main
        5       [4]     RETURN          0 1 0

function <test-local.lua:2> (4 instructions, 16 bytes at 00325BA8)
0 params, 2 stacks, 1 upvalue, 0 locals, 1 constant, 0 functions
        1       [3]     GETUPVAL        0 0 0   ; print
        2       [3]     LOADK           1 0     ; "hello world"
        3       [3]     CALL            0 2 1
        4       [4]     RETURN          0 1 0
Note that in the second version, instead of querying the global table with GETGLOBAL, the function 'main' called GETUPVAL, which retrieve an upvalue by it's index, which is very fast. 

--rb



On 12/12/06, BrillyWu <brillywu@gmail.com> wrote:

In lua baselib.c,it give us a lot of base function,such as:

static const struct luaL_reg iolib[] = {
 {LUA_ERRORMESSAGE, errorfb},
 {"clock", io_clock},
 {"date", io_date},
 {"debug", io_debug},
 {"execute", io_execute},
 {"exit", io_exit},
 {"getenv", io_getenv},
 {"remove", io_remove},
 {"rename", io_rename},
 {"setlocale", setloc},
 {"tmpname", io_tmpname}
};

static const struct luaL_reg iolibtag[] = {
 {"appendto", io_appendto},
 {"closefile", io_close},
 {"flush", io_flush},
 {"openfile", io_open},
 {"read", io_read},
 {"readfrom", io_readfrom},
 {"seek", io_seek},
 {"write", io_write},
 {"writeto", io_writeto}
};

and in my project,I definded a lot of function of myself.and register to
lua.

in Lua script,I can use this function:

test.lua


function main()
   print("hello wolrd");
end function

main();

-----------------------------
I use the function by its funciton name:"print",How can I call print
function,not by its function name,but use the index of the function in the 
array?