Re: Tuples and other constant values
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- Subject: Re: Tuples and other constant values
- From: Daurnimator <quae@...>
- Date: Thu, 9 Jul 2015 10:41:44 +1000
On 9 July 2015 at 08:13, William Ahern <william@25thandclement.com> wrote:
> In the same spirit as Lua's method calling syntax, what about 3) simply
> converting
>
> local v = t[a,b,c]
>
> to
>
> local v = t[a][b][c]
>
> where the compiler inserts the necessary checks for nil tables. Similarly
>
> t[a,b,c] = v
>
> becomes
>
> t[a][b][c] = v
>
> where the compiler autovivifies the intermediate tables, just like in Perl.
> This syntactic sugar would only be useful as a practical matter where the
> number of elements in the tuple-key is fixed, otherwise disambiguiting
> intermediate tables from the value being queried would introduce unnecessary
> complexity in the language and/or the VM. But in some sense that's almost
> preferable, the constraint being akin to strict typing.
I'd prefer we reserved that syntax to just send multiple arguments to
an __index metamethod.
i.e. this would print out '1 2 3'
local t = setmetatable({}, {__index=function(t,...) print(...) end})
_=t[1,2,3]
If a user wanted the vivification they could just do that in their __index:
local vivify_mt = {}
vivify_mt.__index=function(t,k,...)
local v = t[k]
if select("#", ...) == 0 then
return v
end
if v == nil then
v = setmetatable({}, vivify_mt)
t[k] = v
end
return v[...]
end
- References:
- Re: Tuples and other constant values, Cosmin Apreutesei
- Re: Tuples and other constant values, Tim Hill
- Re: Tuples and other constant values, Coda Highland
- Re: Tuples and other constant values, Tim Hill
- Re: Tuples and other constant values, Jay Carlson
- Re: Tuples and other constant values, Daurnimator
- Re: Tuples and other constant values, Tim Hill
- Re: Tuples and other constant values, Dirk Laurie
- Re: Tuples and other constant values, Andrew Starks
- Re: Tuples and other constant values, Philipp Janda
- Re: Tuples and other constant values, William Ahern