Finalized Exceptions
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: Finalized Exceptions
- From: Mark Hamburg <mhamburg@...>
- Date: 2004年8月05日 18:31:59 -0700
I just finished reading Diego Nehab's page on "Finalized Exceptions" on the
Lua Users' Wiki. (http://lua-users.org/wiki/FinalizedExceptions) I like the
overall approach and something like it might be a good idea for inclusion in
Lua 5.1. I would add it myself to my version, but I'm cautious about
namespace clashes.
Here are some general reactions:
* I'm a little unclear as to where the finalized part comes in with respect
to exceptions -- i.e., the title isn't immediately obvious to me.
* The notion of generating a new finalization function and then running
everything else through it feels a little heavy for coding. Yes, it beats
many of the present alternatives, but it cries out for an easy way to wrap a
block of statements in a single try.
* Is my impression correct that try does not work if the code being wrapped
should happen to throw an exception? In other words, it only works if
everything is well behaved?
* One other pattern I use routinely works like this:
get = protect(function( host, path )
return withConnection( host, 80, function( c )
assert( c:send( "GET " .. path .. " HTTP/1.0\r\n\r\n" ) )
-- send the request
-- get headers
local h = {}
while 1 do
local l = assert( c:receive() )
if l == "" then break end
table.insert( h, l )
end
-- get body
local b = assert( c:receive( "*a" ) )
return h, b
end )
return b, h
end)
Where we define:
local function pack( success, ... )
return success, arg
end
withConnection = function( host, port, func )
local c = assert( connect( host, port ) )
local success, results = pack( pcall( func, c ) )
c:close()
if not success then error( results[ 1 ] ) end
return unpack( results )
end
(I left the protect in on get, but it should probably really go on
withConnection in which case it wouldn't really be needed on get.)
This basically mirrors C++ constructor/destructor error handling semantics.
It creates exactly as many closures, but it makes fewer calls to pcall.
Mark