Re: Expression-local variables and 'let'

Quoting Isaac Gouy <[email protected]>:

> > You need "let" so that you can have type inference for local
> > variables:
> >     let x = 5; // okay, infer x's type
> >     y = 5;     // error, y is undeclared
> 
>       var x = 5; // okay, infer x's type

Okay, but I prefer a more functional style so I use "let"/"val" more than var. I
rarely use "var," in fact.

In fact, I wish that formal parameters were immutable by default so that code
like this would not compile:
    void f(int x) {
         for (int i = 0; i < x; ++x) {
            ...
         }
    }
Where, I had meant "++i" instead of "++x." The rationale being that functions
rarely modify their parameters intentionally. 

I also asked for fields to be final by default:

    class X {
        int x;
    }

    void main(String[] args) {
        (new X(x:1).x = 2; // error: X.x is immutable
    }

If you wanted a field to be mutable, you would say:

    class X {
        var int x;
    }

These two changes would get rid of the last cases where "final" means
"immutable" in the language and promote a more functional style. That idea was
shot down a long time ago but maybe it can be revived considering all the
proposed syntax changes in the pipeline.

- Brian




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