Re: [ANN] Lua 5.2.0 (beta-rc1) now available
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- Subject: Re: [ANN] Lua 5.2.0 (beta-rc1) now available
- From: David Manura <dm.lua@...>
- Date: 2011年6月14日 01:04:09 -0400
diffs-lua-5.2.0-alpha-beta-rc1.txt wrote:
> goto, bit32.extract, bit32.replace, load with env, table __gc,
> fractional hex constants, rawlen, ...
ooo
> goto
When a single goto exists inside a conditional block, some of the
JMP's are superfluous:
local x = 1
@a:
if x > 1e8 then goto e end
x = x + 1
goto a
@e:
-- equivalent
local x = 1
while not(x > 1e8) do
x = x + 1
end
$ luac -p -l test.lua
main <t.lua:0,0> (12 instructions at 0x9e0cb78)
0+ params, 2 slots, 1 upvalue, 2 locals, 2 constants, 0 functions
1 [1] LOADK 0 -1 ; 1
2 [3] LT 0 -2 0 ; 100000000 -
3 [3] JMP 0 1 ; to 5
4 [3] JMP 0 2 ; to 7
5 [4] ADD 0 0 -1 ; - 1
6 [5] JMP 0 -5 ; to 2
7 [8] LOADK 1 -1 ; 1
8 [9] LT 1 -2 1 ; 100000000 -
9 [9] JMP 0 2 ; to 12
10 [10] ADD 1 1 -1 ; - 1
11 [10] JMP 0 -4 ; to 8
12 [11] RETURN 0 1
> bit32.extract, bit32.replace
It's curious that these are 0-indexed given
http://lua-users.org/wiki/CountingFromOne . However, 0-indexing is
conventional in bitops.
> luaL_execresult, luaL_fileresult, luaL_getsubtable, luaL_newlibtable, ...
(shrugs)
> <code>modname</code> and an extra value dependent on how it got the loader.
> (If the loader came from a file, this extra value is the file name.)
I'm not sure it's good design practice for modules to know where they
were loaded from. Module packers like preload/squish can transform
modules that are files into modules that are not files:
http://loop.luaforge.net/release/preload.html
http://matthewwild.co.uk/projects/squish/home
> [package.loaded] is only a reference to the real table;
> assignments to this variable do not change the
> table used by <a href="#pdf-require"><code>require</code></a>.
Probably good for sandboxing.
> We use the term <em>sequence</em> to denote a table where all
> integer keys comprise the set <em>{1..n}</em> for some integer <em>n</em>,
...
> In that case, the list must be a proper sequence
...
> in the array lst
list, sequence, proper sequence, array? Is the usage of these terms consistent?
< error handler <code>err</code>.
> message handler <code>msgh</code>.
Rationale for the terminology change?
> 6.5 - Table Manipulation [...]
> a __len metamethod (see §3.4.6). For performance reasons, all table
> accesses (get/set) performed by these functions are raw.
Why is the length operator not likewise raw in table functions?