2011/6/2 Xingzhi Pan
<vengeance.storm@gmail.com>
Hi,
I'm using luac -l to observe the bytecode of the following Lua source:
1 function fo (i)
2 uv = 0
3 function fi1 ()
4 print(uv)
5 uv = 1
6 print(uv)
7 end
8 function fi2 ()
9 print(uv)
10 uv = 2
11 print(uv)
12 end
13 if i == 1 then return fi1 end
14 if i == 2 then return fi2 end
15 end
16
And this is what I get:
main <../upval.lua:0,0> (3 instructions, 12 bytes at 0x100101050)
0+ params, 2 slots, 0 upvalues, 0 locals, 1 constant, 1 function
1 [15] CLOSURE 0 0 ; 0x1001011f0
2 [1] SETGLOBAL 0 -1 ; fo
3 [15] RETURN 0 1
function <../upval.lua:1,15> (15 instructions, 60 bytes at 0x1001011f0)
1 param, 2 slots, 0 upvalues, 1 local, 6 constants, 2 functions
1 [2] LOADK 1 -2 ; 0
2 [2] SETGLOBAL 1 -1 ; uv
3 [7] CLOSURE 1 0 ; 0x1001015c0
4 [3] SETGLOBAL 1 -3 ; fi1
5 [12] CLOSURE 1 1 ; 0x1001017c0
6 [8] SETGLOBAL 1 -4 ; fi2
7 [13] EQ 0 0 -5 ; - 1
8 [13] JMP 2 ; to 11
9 [13] GETGLOBAL 1 -3 ; fi1
10 [13] RETURN 1 2
11 [14] EQ 0 0 -6 ; - 2
12 [14] JMP 2 ; to 15
13 [14] GETGLOBAL 1 -4 ; fi2
14 [14] RETURN 1 2
15 [15] RETURN 0 1
function <../upval.lua:3,7> (9 instructions, 36 bytes at 0x1001015c0)
0 params, 2 slots, 0 upvalues, 0 locals, 3 constants, 0 functions
1 [4] GETGLOBAL 0 -1 ; print
2 [4] GETGLOBAL 1 -2 ; uv
3 [4] CALL 0 2 1
4 [5] LOADK 0 -3 ; 1
5 [5] SETGLOBAL 0 -2 ; uv
6 [6] GETGLOBAL 0 -1 ; print
7 [6] GETGLOBAL 1 -2 ; uv
8 [6] CALL 0 2 1
9 [7] RETURN 0 1
function <../upval.lua:8,12> (9 instructions, 36 bytes at 0x1001017c0)
0 params, 2 slots, 0 upvalues, 0 locals, 3 constants, 0 functions
1 [9] GETGLOBAL 0 -1 ; print
2 [9] GETGLOBAL 1 -2 ; uv
3 [9] CALL 0 2 1
4 [10] LOADK 0 -3 ; 2
5 [10] SETGLOBAL 0 -2 ; uv
6 [11] GETGLOBAL 0 -1 ; print
7 [11] GETGLOBAL 1 -2 ; uv
8 [11] CALL 0 2 1
9 [12] RETURN 0 1
So my question is that for inner functions fi1 and fi2, why GETGLOBAL
and SETGLOBAL, rather than GETUPVAL and SETUPVAL, are used? Isn't uv
an upvalue?
Currently, uv is a global variable.
If you want an upvalue, you must use 'local uv = 0' line 2.
François
Also, it shows "0 upvalues" for these 2 functions, where I thought
should be one.
Thanks,
Xingzhi 'Harry' Pan
