brian.goetz at oracle.com
Mon Mar 3 09:45:14 PST 2014
So, none of these are really "tweaks". And of these, only #1 is
actually small. Some very quick comments.
> *Idea #1: Allow final index variable in Iterable loops*
OK, this is a pretty tiny change. Low cost, low risk -- but also low
> *Idea #2: Allow non-this code prior to super()/this() call in
This is well-traveled ground; this request has come up, and been shot
down, many times. If anything, the language spec is already too loose
here, allowing too many unsafe operations (e.g., calling virtual methods
from constructors, allowing constructor to publish 'this', etc) and this
would make this problem dramatically worse.
Worse, of the cases where people claim they need this feature, they tend
to be wrong most of the time, both underestimating the safety costs and
overestimating the need. In your example, you can accomplish what you
want both safely and without redundant computation with a combination of
a public factory and a private constructor. Weakening the language
safety is not the answer.
> *Idea #3: Allow generic type declarations wherever normal type
> declarations are allowed*
Obviously "wherever normal type declarations" is broader than you mean.
What you're looking for is the ability to "uncapture" a captured
variable, giving it a name. As you've pointed out, generic methods
already provide you the ability to do that, and what you're asking for
is do to that 'inline' in a block of code. My recommendation is to try
and take this to the next step (a more detailed analysis); I think
you'll find you'll run into complexity at multiple levels.
> *Idea #4: Teach compiler that an exception means the last assignment
> statement was not executed*
I'm kind of sympathetic here. Specifying "unless the last statement
is..." is kind of messy, increasing the cost.
> *Idea #5: Allow enum types to have generic type parameters*
Another frequent suggestion. I agree it would have been better if it
were done this way initially, and the cost would have been low. The cost
of doing this now in a binary-compatible way would be higher.
> Some of these obviously would take more compiler work than others.
> However, I want to make sure to keep separate feedback based on
> practical concerns (e.g., "too hard to implement") vs. more
> fundamental language issues that I may be missing.
1, 4: practical, but probably low return on investment
2: bad idea
3: bigger than you think
5: desirable, but compatibility risks lurk
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