Re: Yet another proposal for <toclose> (was Re: [ANN] Lua 5.4.0 (alpha) now available)
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- Subject: Re: Yet another proposal for <toclose> (was Re: [ANN] Lua 5.4.0 (alpha) now available)
- From: Sergey Kovalev <kovserg33@...>
- Date: 2019年6月28日 16:05:38 +0300
Why we need extra functionality if it could be done with existing one?
> do
> -- --------------------------------------------------------------
> -- 'scope' is like 'local' in that the variable is local to the
> -- current scope, but unlike 'local', the variable is closed at
> -- the end. When we leave the current scope, each variable
> -- declared as a 'scope' is checked for a __close metamethod, and
> -- if it exists, it is called; otherwise, nothing happens.
> -- --------------------------------------------------------------
>
> scope f,err = io.open("foobar")
> local x,y,z -- regular locals
>
> -- -----------------------------------------
> -- all variables of type 'scope' are closed
> -- -----------------------------------------
> end
function scope(body)
local list,res={}
local function auto(close,msg)
return function(t)
if type(t)~='table' then error("need table: { expression }",2) end
if t[1] then table.insert(list,{ arg=t[1], fn=close or io.close })
else
if msg=='weak' then return table.unpack(t,2) end
error(msg or t[2] or "no resource",2)
end
return table.unpack(t)
end
end
local ok,err=pcall(function() res={body(auto)} end)
for i=#list,1,-1 do list[i].fn(list[i].arg) end
if not ok then
if type(err)~='string' then error(err,2)
else error("scope error\nlua: "..err,2) end
end
return table.unpack(res)
end
scope(function(auto)
local f=auto(io.close){ io.open "foobar" } -- will be closed
local g,err=auto(io.close,"weak"){ io.open "foobar2" }
local x,y,z -- regular locals
end)