const sucks

[Andrei Alexandrescu]

Dave wrote:
> "Andrei Alexandrescu" <SeeWebsiteForEmail at erdani.org> wrote in message
> news:gd85n2$9rq$1 at digitalmars.com...
>> Just got this from Eric Niebler:
>>
>> http://tinyurl.com/4apat7
>>
>> Guess what Anders Heljsberg and Guy Steele have to say about future of
>> programming languages.
>>
>> Immutable and eliminating side effects are necessary. Quickly written 
>> down
>> from Anders: "...we need support for immutable data at the language
>> level..." "...so that the compiler can infer that there is isolation..."
>> "... formalization of immutability... we don't have them in the language
>> and it's nontrivial to put them in... and that's the big challenge." He
>> goes on and describes the difficulties... and mentions "pure functions"
>> and "transitivity" and "functional extensions"!!! "Pure FP is not the
>> solution... what we try to do is to have islands of purity in functional
>> style and switch between default to functional in a hybrid style of
>> programming... the answer is not at the extreme..."
>>
>> This is huge. You have to listen to it to hear just how huge it is. He is
>> essentially describing some of the difficulties we have encountered and
>> already solved in D2, so it looks we have a strategic advantage.
>>
>> This is the confirmation I hoped was going to come someday. If it
>> surprises me, it that it comes so early, so unequivocally, and so aligned
>> terminologically. I'm in Nirvana.
>>
> 
> Anders mentioned "... be clearer about where the mutation occurs and 
> where the side-effects are, by in a sense switching the default to be 
> more functional".
> 
> Should D3 be the version that introduces default immutable storage and 
> default pure functions?
> 
> IIRC, this was discussed for D2 early on in the const discussion, but 
> the consensus then was that it was too big of a leap for an imperative 
> language.

I'm very glad someone finally answered about the main thrust of the 
interview. I was a tad let down by the thundering silence following my 
post, which I attributed to its rather strident tone; in my defense, I 
have to say I was in a state of euphoria caused by such a comprehensive 
confirmation of beliefs and thinking patterns I held dear for years.

That aside, I do highly recommend interested people to watch the video. 
It is slow and boring at times, but some very interesting points are 
being made, particularly about the relationship between manycores and 
immutability (fortunately, that's also towards the beginning of the 
interview). It sure makes D look like it placed a winning bet two 
(three?) years ago when we started working on immutability.

To answer your point, Dave, I think the alea has been jacta with regard 
to D's flavor. We'll be unable to retire mutability as a matter of 
course, otherwise we might as well call the new language E :o). What we 
can do is to simplify introduction of places and regions where 
immutability is either a must, or the default. Also, we can better 
separate the places where mutability is harmless (stack data) from 
places where mutability causes problems (shared data). Walter is in fact 
working on language changes in that general direction.


Andrei