Re: new "empty" value/type in Lua?
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- Subject: Re: new "empty" value/type in Lua?
- From: Scott Fial <scott@...>
- Date: 2013年7月03日 22:12:11 -0700
On 7/3/2013 9:46 PM, Scott Fial wrote:
What if there was a formal way to set/get the internal "default value"
of a table? For example, if I were to call setdefault(t, -1), then t
could contain any value except -1. Reading a non-existent key would now
return -1. Assigning -1 to a key would delete it.
Scott
Continuing this thought. For convenience, "table" could provide the
basic functions and a pre-made "undef" atom for general use as an
alternative default:
function table.getdefault(t) --[[ magic ]] end
function table.setdefault(t, d) --[[ magic ]] end
function table.has(t, k) return t[k] ~= table.getdefault(t) end
function table.delete(t, k) t[k] = table.getdefault(t) end
table.undef = {__tostring = function () return "undef" end}
setmetatable(table.undef, table.undef)
Scott
- References:
- Empty? No. Array? No. Has? Yes., Dirk Laurie
- Re: Empty? No. Array? No. Has? Yes., steve donovan
- Re: Empty? No. Array? No. Has? Yes., David Heiko Kolf
- Re: Empty? No. Array? No. Has? Yes., Roberto Ierusalimschy
- Re: Empty? No. Array? No. Has? Yes., Eike Decker
- Re: Empty? No. Array? No. Has? Yes., Coda Highland
- Re: Empty? No. Array? No. Has? Yes., Andrew Starks
- Re: Empty? No. Array? No. Has? Yes., Eike Decker
- Re: Empty? No. Array? No. Has? Yes., Andrew Starks
- Re: new "empty" value/type in Lua?, Scott Fial