Re: (not) handling new programming idioms with grace

[Pierre Chapuis <catwell@...>]

> I don't quite understand the problem, and maybe my ignorance shows,
> but ...
> 
> What does a 'with' structure achieve that
> 
> repeat
>   local whatever
> ...
>   if exception then break end
> ...
> until false
> 
> does not?

I don't really get how this is similar to "with". The goal of "with" (i.e Python Context Managers [1]) is to make sure that something is executed at the beginning of a code block and something else at the end. So it would be more something like this in Lua terms:

    with foo do
        -- stuff
    end

... works a bit like...

    do
        foo:__enter()
        -- stuff
        foo:__exit()
    end

... except `__exit` is called no matter what happens in "stuff", including all those cases:

    -- foo:__exit() is called once
    local function f(foo)
        with foo do
            return
        end
    end

    -- foo:__exit() is called twice
    for i = 1, 5 do
        with foo do
            if i == 2 then
                break
            end
        end
    end

    -- foo:__exit()  is called once
    with foo do
        error()
    end

This is important when you write code that deals with a resource that has to be released immediately and not asynchronously so you cannot rely on `__gc`, e.g. a database transaction, a mutex, arguably some file descriptors...

[1] https://docs.python.org/2.5/whatsnew/pep-343.html