Re: Implicit Table Indexing/Creation
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- Subject: Re: Implicit Table Indexing/Creation
- From: Gavin Kistner <gavin@...>
- Date: 2007年3月20日 21:36:20 -0600
On Feb 22, 2007, at 6:37 PM, William Ahern wrote:
I thought I had spotted a patch awhile ago which came across this
list.
It basically allowed for syntax like:
local t, v;
v = t.something.innerthing
In this case v would be nil, and the interpreter wouldn't get upset.
Likewise,
t.something.innerthing = "foo"
would implicitly create the table t.something.
Is there a patch against 5.1 for this? Basically, amongst other less
shallow reasons, I'd much rather be able to do
proc.slaves.max = 10
proc.slaves.min = 3
rather than
proc = {}
proc.slaves = { max = 10, min = 3 }
which is still nicer than
proc = {
slaves = {
max = 10,
min = 3
}
}
Abstractly the namespace of the configuration is hierarchical, but
usually its nice to pretend its flat. And to do that the language
needs
to play along.
This doesn't exactly match your needs, but perhaps it's close enough?
Lua 5.1 Copyright (C) 1994-2006 Lua.org, PUC-Rio
> autotable = {
>> meta = {
>> __index = function(t,k)
>> local auto = autotable()
>> t[k] = auto
>> return auto
>> end
>> }
>> }
> function autotable:new( )
>> local t={}
>> setmetatable(t,self.meta)
>> return t
>> end
> setmetatable( autotable, { __call = autotable.new } )
> proc = autotable()
> proc.slaves.max = 10
> proc.slaves.min = 3
> for k,v in pairs( proc ) do print( k,v ) end
slaves table: 0x30c260
> for k,v in pairs( proc.slaves ) do print( k,v ) end
max 10
min 3
> _ = proc.oops
> for k,v in pairs( proc ) do print( k,v ) end
oops table: 0x30d080
slaves table: 0x30c260
As you can see, you a) need to tell it when you want an autotable.
(You can't just say "local t" and have dereferencing it automatically
make it into t table. That's just crazy talk, IMO.) Also, simply
asking for a property necessarily instantiates it.