Re: [ANN] Lua 5.4.0 (alpha) now available

["Soni \"They/Them\" L." <fakedme@...>]

On 2019-06-20 6:13 p.m., Patrick Donnelly wrote:
> On Thu, Jun 20, 2019 at 2:07 PM Dibyendu Majumdar
> <mobile@majumdar.org.uk> wrote:
> >
> > On Thu, 20 Jun 2019 at 21:59, Patrick Donnelly <batrick@batbytes.com> wrote:
> > >
> > => > 2) With regards to the 'toclose' variable declaration, introducing a
> > > > 'with' statement is the nicest approach.
> > > >
> > > > with <vars> = <initializers> do
> > > >
> > > > end
> > > >
> > > > This idiom is familiar to most programmers who use Python.
> > > > BTW @Patrick Donnelly this has nothing to do with Python's reasons for it etc.
> > >
> > > Quoting myself from the prior thread:
> > >
> > > "I want to point out the reasons why Python requires a control
> > > structure but Lua would not: Python's locals are function-scoped.
> > > Declaring a local in Python means it doesn't go out of scope until the
> > > function returns. For this reason, Python requires an explicit control
> > > structure to define the lifetime of the variable. Lua does not have
> > > this limitation."
> > >
> > > They absolutely needed another control structure to implement their
> > > flavor of RAII.
> > >
> >
> > And I repeat that the suggestion to use this syntax doesn't have
> > anything to do with why Python had to have it. It is a nice idiom used
> > in many languages. C# calls it 'using'. In Java we have try with
> > resources. But all are the same construct.
>
> Fine, but I haven't seen a good argument for __enter so a "with"
> construct looks unnecessary, distracting, and unnecessary indentation.

a "with" construct is unnecessary even with __enter, and I'd argue it'd 
be beneficial to have __enter without "with": assignment to a toclose 
variable (or uh, a with variable) would cause __enter, and when it goes 
out of scope, an __close.

e.g. let's say you want a function that can be passed a file directly or 
as part of a larger processing chain:

local function do_something_with_file(f)
    local <with> f = f -- f:__enter()
    f:write("hello!\n")
    -- f:__close()
end

do_something_with_file(io.open("foo", "w")) -- okay, file gets closed

local <with> f = io.open("bar", "w") -- f:__enter()
do_something_with_file(f) -- doesn't close file
f:write("goodbye!\n")
-- f:__close() -- file gets closed