New candidate JEP: 443: Unnamed Patterns and Variables (Preview)

[Brian Goetz]

On 3/21/2023 5:39 PM, Holo The Sage Wolf wrote:
>
> Is there a reason not to allow implicit Unnamed Variables in 
> try-with-resources and Catch-block?
>

The JEP already describes these cases:


      Unnamed variables

The following kinds of declarations can introduce either a named 
variable (denoted by an identifier) or an unnamed variable (denoted by 
an underscore):

  * A local variable declaration statement in a block (JLS 14.4.2),
  * A resource specification of a|try|-with-resources statement (JLS
    14.20.3),
  * The header of a basic|for|statement (JLS 14.14.1),
  * The header of an enhanced|for|loop (JLS 14.14.2),
  * An exception parameter of a|catch|block (JLS 14.20), and
  * A formal parameter of a lambda expression (JLS 15.27.1).


Try with resources, and catch blocks, are listed as places where you can 
use unnamed variables.  Am I undersatnding your question properly?



> To allow:
>
> |try (Scope.open()) { ... } --- try { ... } catch (Exception) { ... } |
>
> to be implicitly
>
> |try (var _ = Scope.open()) { ... } --- try { ... } catch (Exception 
> _) { ... } |
>
> Unlike a normal expression, and expression on the RHS of a 
> try-with-resources variable has an explicit context, there is no fear 
> of someone forgetting the result of the expression by mistake.
>
> In a Catch block the exception is uniquely accessible through the 
> variable declared in the declaration of the block, so there is no fear 
> that someone will get confused by this implicitness.
>
> This implicitness will make stuff like logging context, which is far 
> from a niche use case, much more elegant.
>
>
> On Tue, Mar 21, 2023 at 9:17 PM Mark Reinhold 
> <mark.reinhold at oracle.com> wrote:
>
>     https://openjdk.org/jeps/443
>
>       Summary: Enhance the Java language with unnamed patterns, which
>     match
>       a record component without stating the component's name or type,
>       and unnamed variables, which can be initialized but not used. Both
>       are denoted by an underscore character, _. This is a preview
>     language
>       feature.
>
>     - Mark
>
>
>
> -- 
> Holo The Wise Wolf Of Yoitsu
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