lambda expression parameters

[Zhong Yu]

On Tue, Dec 18, 2012 at 8:15 PM, Dan Smith <daniel.smith at oracle.com> wrote:
> On Dec 18, 2012, at 5:43 PM, David Holmes <David.Holmes at oracle.com> wrote:
>
>> I don't grok the problem. If the parameter is not modified then it is
>> effectively final. Making parameters final is then only an
>> error-detection mechanism, and I don't see that is warranted in lambda
>> expressions. So I don't see "final by default" as warranted.
>>
>> Having to add back the inferred type to enable final to be added doesn't
>> seem like a large burden.
>
> Yeah, I think I agree with David.  The times when it seems most useful to say "this parameter is final and I definitely don't want anyone changing it" are when you've got a large lambda body, and then it's really not so painful to give your parameters full declarations ('final String s').
>
> It's worth noting that 'final' parameters and local variables didn't exist in the original language and were only added to support the "captured variables must be final" rule when anonymous/local classes were added.  If "effectively final" were an option back then (don't know if it's something they thought about or not), I would bet we still wouldn't have 'final' parameters and local variables.  They're really a lot less useful than 'final' fields -- because all interaction is in a single thread and within a single block of code.

Agreed, although most method parameters and many local variables are
conceptually final, people don't bother to mark them final.

Making method parameters implicitly final is inconsistent with
existing practices; the benefit is dubious:

If a programmer assigns a new value to a method parameter, and later
reads it, it is very likely intentional, there's no need for alarm
here.

If a programmer assigns a new value to a method parameter, and never
reads it, it is probably a mistake; fortunately IDEs will raise a
warning for it.

Zhong Yu

>
>> On the other hand can't the compiler accept
>> parameter modifiers even if it infers the type?
>
> No, there are two syntax options: list of identifiers, or full method parameter list.  Less complex that way.
>
> —Dan
>