Re: "+="

[Luiz Henrique de Figueiredo <lhf@...>]

>From: Gavin Wraith <gavin@wraith.u-net.com>

>Am I right in thinking that the Lua VM does two
>lookups in executing something like
>"a.b.c.d.e.f = a.b.c.d.e.f + 57" ?

Yes. Here is the code for a.x=a.x+57

main <@(stdin):0> (15 bytes at 0x80530d8)
     0  04        STACK           4
     1  00        ARGS            0
     2  0F00      GETGLOBAL       0     ; "a"
     4  0B01      PUSHCONSTANT    1     ; "x"
     6  0F00      GETGLOBAL       0     ; "a"
     8  1201      GETDOTTED       1     ; "x"
    10  0739      PUSHNUMBER      57
    12  25        ADDOP
    13  1A        SETTABLEPOP
    14  00        ENDCODE


>This is presumably something which any language
>must address which allows complex L-value
>expressions. Any plans for this in a future
>release? 

You have to keep in mind that getting and setting values in tables
may trigger tag methods and so an update operation like 'a.x += 57' really
is more complicated than it seems.

There are two reasons for wanting += : readability and efficiency.
I agree with readability but not with efficiency. Lua is already very fast
and even faster in the next version.
--lhf