Concise method body + type inference ?

[Remi Forax]

----- Mail original -----
> De: "Alex Buckley" <alex.buckley at oracle.com>
> À: "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
> Envoyé: Jeudi 4 Octobre 2018 02:30:12
> Objet: Re: Concise method body + type inference ?

> On 10/3/2018 4:06 PM, John Rose wrote:
>> On Oct 3, 2018, at 3:56 PM, Alex Buckley <alex.buckley at oracle.com
>> <mailto:alex.buckley at oracle.com>> wrote:
>>>
>>> Let's say that Java 5 had the right idea by coupling an overriding
>>> method to an overridden method, via @Override. Then, your proposal is
>>> at odds with Java 5, because omitting the method signature of the
>>> overriding method also means omitting @Override. (I assume you
>>> intended for there to be no annotations on your lambda-like method
>>> bodies such as `hashNext() -> index < end;`)
>>
>> Put another way, Remi's suggestion is for a coupling stronger
>> than @Override, which is purely advisory.  An 'override'
>> modifier would upgrade the advice to something mandatory,
>> at which point types might from from the super.
> 
> If you write @Override, then it's not just advice to the compiler that
> you intend to override something; it's a statement that you DO override
> something. You get a compile-time error if you don't. It's an `override`
> modifier in all but spelling.
> 
> But yes, Remi is saying that some method declarations have become so
> full of redundant information -- the signature types, the accessibility
> modifier, the @Override annotation, the {} and `return` for the body --
> that it's time to reject the redundancy and go for concision not only in
> the body but in the declaration as a whole.
> 
> Brian has already made the argument to infer only within the method's
> implementation -- meaning within the method's body, not for the method
> declaration as a whole. I think Remi views the whole method declaration
> as "implementation", of the overridden method, and concludes that
> inferring the signature et al is reasonable. But it's rather arbitrary
> to give an overriding method the sole right to a concise declaration,
> and not a `private` method, a `final` method, a `default` method, etc.

arbitrary => You have to find the parameter types somewhere, that's why it's (quote) arbitrary (quote), exactly like a lambda requires a functional interface (emphasis on the interface), concise declaration only works when there is already a declaration.
An abstract method, a concrete method that is overriden, a default method, all provides the necessary information so the implementation can use the concise declaration.

i will just add that if you take a look to a lambda, a lambda is already a way to define a concise declaration, the parameter types of the lambda is also inferred from the declaration of the abstract method of the functional interface. So the idea of the concise declaration is not alien to Java (at least Java 8+), it's a way to recognize that we can extend the inference of the parameter types to all methods that provides an implementation, not the lambda only.
it's a growing a language thing, we already have concise declaration for lambdas and we enhance it to works on any methods that provides an implementation.

> 
> Alex

Rémi