Optional brackets around lambda expression (was: Expecteddistribution of lambda sizes)

[Reinier Zwitserloot]

If all ambiguity must be avoided, all mathematical expressions would be very
awkward; only 2-arg arithmatic would be legit as anything else is
potentially ambiguous. We have precedence rules for a reason; it's so we can
write a + b * c and not be forced to parenthesize something.

The most intuitive precedence, to me anyway, is that lambdas are very greedy
(i.e. low precedence). The longest possible expression following the #() is
all part of the lambda's expression.

In practice this works out, because almost all the symbols cannot legally be
applied to a function object anyway - only + can (and is rarely if ever what
you wanted), and deref, which is also in practice rarely what you want, as
there's very little point in defining a closure and then immediately
executing it.

We could throw some curveballs out there and ask random java programmers
what they think the precedence order would be, something like:

"" + #(String a) a.length() + 5


And ask them if this prints "Function(String)int5" or "Function(String)int".
If I was a gambling man I'd guess that the (vast) majority of java
programmers will correctly guess "Function(String)int".

 --Reinier Zwitserloot



On Fri, Jun 17, 2011 at 1:11 PM, <david.moss at ubs.com> wrote:

>
>
> > As discussed in another thread; it's just like strawman, except
> > the parentheses around the expression are optional. Thus,
> > official strawman wants this:
> >
> > Comparable<String> comparator = #(a, b) (a.length() - b.length());
> >
> > and the paren-less variant lets you write this instead:
> >
> > Comparable<String> comparator = #(a, b) a.length() - b.length();
>
> Hi,
>
> Seems to me this is ambiguous; you could have the following situation,
> for instance:
>
> String b = "some";
> Comparable<String> comparator = #(a, b) a.length() - b.length();
>
> And not know whether it should be read as:
>
> String b = "some";
> Comparable<String> comparator = (#(a, b) a.length()) - b.length();
>
> Or:
>
> String b = "some";
> Comparable<String> comparator = (#(a, b) a.length() - b.length());
>
> Kind Regards,
>
> David.
>
> --
>
> David S. Moss
> Stress Testing Tool Lead Developer
> IT Risk
> 1923 96757
>
> --
>
> Sent from my Dell Optiplex 745
> Based on the present E-Mail exchange, and/or on the agreement reached
> with you, respectively, UBS is entitled to contact you via insecure
> E-Mail:
> (a) E-Mails contain substantial risks such as lack of confidentiality,
> manipulation of content and sender, misdirection, viruses etc. UBS
> does not accept any liability for damages arising from use of
> E-mail. Accordingly, UBS recommends to abstain from sending any
> sensitive information via E-Mail, from forwarding the text received
> when submitting reply E-Mails and recommends to manually capture the
> E-Mail address in every instance. If you should wish to verify the
> content of this message, please request a hard-copy version.
> (b) In principle, UBS does not accept any (purchase) orders,
> cancellation of orders or authorizations etc. via E-mail. If UBS
> receives such E-Mails, UBS is not obliged to expressly decline them.
> If you have received this E-Mail by mistake or do not wish to be
> contacted by E-Mail in the future, you are kindly asked to inform UBS
> accordingly. Any E-Mail received by mistake (including all its annexes)
> needs to be destroyed and the content may not be forwarded nor disclosed
> to any further persons.
> c) This message is provided for informational purposes and should not be
> construed as a solicitation or offer to buy or sell any securities or
> related financial instruments.
>
> UBS reserves the right to retain all messages. Messages are protected
> and accessed only in legally justified cases.
>