Final by default?

[Mike]

On Wednesday, 12 March 2014 at 23:51:41 UTC, bearophile wrote:
> Walter Bright:
>
>> The argument for final by default, as eloquently expressed by 
>> Manu, is a good one. Even Andrei agrees with it (!).
>>
>> The trouble, however, was illuminated most recently by the 
>> std.json regression that broke existing code. The breakage 
>> wasn't even intentional; it was a mistake.
>
> Making final by default is a intentional and planned change, 
> first you introduce "virtual" (it's already present in dmd 
> 2.066alpha), then you give a warning, and then you deprecate 
> things, and then later you generate errors. This gives time to 
> people to fix the code. Even languages far older and far more 
> widespread than D change, like the nullptr of C++ that replaces 
> the 0 as null pointer. People that use D for production code 
> should expect to give a look at the changelog every time a D 
> version comes out and fix the code accordingly. I am keeping a 
> large amount of D2 code updated and introducing the usage of 
> "virtual" in my code will take an amount of time that is little 
> compared to actually writing new code, refactoring code for 
> other purposes, fixing bugs, etc. I don't think you can write D 
> code today and expect it to work perfectly years from now. You 
> have to keep your code updated or keep using the same compiler 
> version.
>
> We can introduce ways to better manage the change, like the 
> "deprecate" keyword, introducing a refactoring tool like the 
> one in Go language, and keep some backwards incompatible 
> changes that the community and you regard as sufficiently 
> important (like deprecating some usages of the comma operator, 
> etc).
>
> I don't even care much about "final by default".
>
> Also in D there are several features that are "going to be 
> deprecated". Like old style operator overloading, the built-in 
> sort, and more and more. Keeping such things in the language 
> for years without even a deprecation messages is bad. In the 
> D.learn newsgroup I keep saying to people "don't use that, it's 
> going to be deprecated". People use those things and if someday 
> they will get actually deprecated they will cause a damage, 
> perhaps comparable to introducing final by default. So please 
> add deprecation messages now for all things that should be 
> deprecated.
>
> Bye,
> bearophile

+1