Re: 5.2: equality for closures
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- Subject: Re: 5.2: equality for closures
- From: Sean Conner <sean@...>
- Date: 2011年6月29日 02:41:58 -0400
It was thus said that the Great Lorenzo Donati once stated:
>
> Sorry for expressing my thought so badly, but mine was a sort of
> half-baked "philosophical" rambling on Lua design about userdata :-)
>
> So any enlightment is welcome (I only played shortly with C API and
> although I know C, I cannot really call myself a C programmer, thus it
> may well be that I missed completely the point of userdata and why their
> usefulness is limited to C side!)
It's used to add support for other data types. I have code that
implements network addresses as a "userdata" for Lua [1]. I can do things
like:
addr = net.address("192.168.1.10",'http')
print(addr.family) -- prints 'ip'
print(addr.addr) -- prints '192.168.1.10'
print(addr.port) -- prints 80
But more importantly, allow me to do stuff like:
addr2 = net.address("fe00::1",33)
print(addr) -- prints 'ip:192.168.1.10:80'
print(#addr) -- prints 4
print(#addr2) -- prints 16
if addr == addr2 then print "They are the same" end
-- won't print anything as they're not the same family [2],
-- not the same address, nor the same port. [3]
-spc (Think of it as a way of mapping a C structure into Lua)
[1] Why not use Luasockets? Because it only supports IPv4, and is a
huge amount of code for what I need.
[2] I support IP, IPv6 and Unix domains.
[3] For those wondering, it's a userdata with the following metatable
fields set:
__index
__tostring
__len
__eq
__lt
__le