request switch statement with common block

[Walter Bright]

On 8/3/2013 1:06 PM, JS wrote:
> On Saturday, 3 August 2013 at 19:22:53 UTC, Walter Bright wrote:
>> On 8/3/2013 12:00 PM, JS wrote:
>>> What I really don't get it is why people think that just because they won't use
>>> such a feature then it must be useless to everyone else.
>>
>> You could provide supporting evidence by examining every use of switch in the
>> dmd, phobos, and druntime source code, and see what percentage of those would
>> benefit from your proposal.
>
>
> This is illogical. The code wasn't written with such a semantic in mind so it
> would require me to rewrite the library to see how useful it truly is.

There are two kinds of semantic language improvements:

1. one that is transformative to programming style, i.e. you'd write your 
program in a fundamentally different way, like OOP.

2. one that is automating an existing pattern, which is finding a recurring 
pattern in code and providing syntactic sugar for it. The foreach loop is in 
this category.

Your proposal looks to me like (2), in fact, you wrote:

> Since the transformation is rather trivial

which supports that categorization.

So, to make automating an existing pattern worthwhile, there ought to be a 
significant percentage of code exhibiting that existing pattern.

For example, bearopile listed:

     enum mysize(T) = T.sizeof;

which does automate a commonly recurring pattern.

> You see how difficult is for me to "sell" it.

Yes, and it should be difficult to sell a new language feature.


> For example, suppose what I am suggesting has zero cost to implement and
> maintain...
>
> Would you allow it in D?

There's no such thing - and certainly your proposal is not. Any syntactic change 
requires an ongoing cost in:

1. implementation
2. maintenance
3. testing
4. documentation
5. users have to learn it
6. books and tutorials about D have to discuss it

Repeat steps 1..6 for every tool that deals with D source code.

Therefore, there needs to be an advantage to it that outweigh all of that. It's 
a high bar. This is true for every language out there, and if you invent your 
own language, you'll quickly start applying that criteria as well.