.... but the either is noise when "file found" and "file not found"
are NOT equally likely. There's no way to know as an API designer. The
one thing you can tell is that "file found" is pretty much always
going to be a reasonable option. No one is going to call fileOpen when
they know for sure it'll fail, there wouldn't be any point. Your
further comment that the "catch" will start drifting away makes no
sense to me. Let's look at the either example again:
You're *calling a different method* to handle the actual result
("doSomethingWithFile"). If that's how we're going to handle it, we
should be fair and let the try/catch example also use that. But, then
the 'catch' for the fileOpen failure is NEVER going to drift away too
far. If you're _not_ going to be calling a different method, the
pattern matching version is going to make the case Right drift away
just as far. This is yet another case where you see (and say, as if
you're some sort of authority) that some way that java can't do is
better, where its actually just personal preference.
Then there's "Left" and "Right" which are just ugly, and which also
suggest there's only 1 type of exception that fileOpen can throw. try/
catch does not suffer from any of these problems.
I don't understand why this thread has drifted into "try/catch itself"
is bad. It started with "forcing onto a programmer the need to check
certain exceptions based on method signatures is not a good idea"
which most seem to agree with. That's entirely different from the idea
that try/catch itself is bad.
On Sep 22, 2:34 pm, Kevin Wright <[email protected]> wrote:
> Lets compare...
>
> Apologies for using Scala, my intent here is to demonstrate the differences
> in the techniques using a language that supports both styles, not
> specifically to advocate Scala.
>
> val fileName = """c:\autoexec.bat"""
>
> // using either
> fileOpen(fileName) match {
> case Left(handle) => doSomethingWithFile(handle)
> case Right(error) => logError(error)
> }
>
> //using try/catch
> try {
> val handle = fileOpen(fileName)
> doSomethingWithFile(handle)
> } catch {
> case Exception(e) => logError(e)
> }
>
> The try/catch example has a couple of extra lines, but that's hardly
> significant. More importantly, as the amount of code grows between the try
> and the catch, possible points of divergence for control flow become
> increasingly unclear. This is high-risk for
> causing maintenance difficulties in the future. using Either, on the other
> hand, suggests that "file found" and "file not found" are equally valid
> non-exceptional outcomes, and places them on a level footing as regards the
> flow of control.
>
> On 22 September 2010 13:19, Ricky Clarkson <[email protected]> wrote:
>
>
>
>
>
> > The point is that it's your choice what to do. Using Either does not mean
> > you have to write lots of if statements, though you can if you like.
>
> > On Wed, Sep 22, 2010 at 12:22 PM, Miroslav Pokorny <
> > [email protected]> wrote:
>
> >> How is either any better than letting catching an exception or letting the
> >> code continue in the original spot. One gets a split off into a everythings
> >> ok here a file, or jump to there and process the problem ? Using Either
> >> ends
> >> up being "more" code because we get the branch for free with
> >> exceptions...And given FileCreation failed is an exception the flow will be
> >> most likely at least a bit different. Continuing on and checking later does
> >> not seem to make much sense most of the time.
>
> >> --
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> --
> Kevin Wright
>
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> pulse / skype: kev.lee.wright
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