Implicit Record Was: JEP draft: Implicit Classes and Enhanced Main Methods (Preview)

Brian Goetz brian.goetz at
Mon Feb 20 20:33:34 UTC 2023

> As i said earlier, it does not work because fields and local variables 
> have different semantics,
> fields are initialized with a default value while local variables need 
> to be initialized before use.
> So the curtain is just a veil that will be pierced by any students 
> moving declarations around.

Of course it "works", it just might not work how you would prefer it to.

Prior to learning about fields, the user can perceive local variables 
(declared in a method) and "shared" variables (accessible to all members 
of the class.)  They can learn about their characteristics.  Then, when 
they learn about classes and fields and accessibility, they can learn 
that the variables they were calling "shared" are really fields.  The 
distinction between locals and fields is there from the beginning, 
though for most use cases, they will not notice the difference.  When 
they're ready to learn the fine differences, there's not anything to 

> From my personal experience, unifying local variable and field leads 
> to more pain than gain, mostly because local

Who said anything about unification of fields and locals?  Where did you 
get such an idea that this is what is being proposed?

First students will learn about statements.  Then they will probably 
learn about local variables.  They can be taught that they disappear 
when the method exits, and each invocation of the method gets a fresh 
copy.  Then they can learn about multiple methods, and then that there 
are variables that can be shared across methods and retain their values 
across method invocations, and while their declaration syntax is the 
same (they're both variables, after all), the _place_ in which they are 
declared is different (which is what makes them shared), and shared 
variables have slightly different characteristics (though not so 
different they have to learn this immediately).  They can learn the 
characteristics of shared variables when it makes sense to teach this.  
And when the curtain is pulled back, they learn all fields have the 
characteristics of these shared variables.

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