The demise of T[new]

[downs]

dsimcha wrote:
> == Quote from downs (default_357-line at yahoo.de)'s article
>> Walter Bright wrote:
>>> The purpose of T[new] was to solve the problems T[] had with passing T[]
>>> to a function and then the function resizes the T[]. What happens with
>>> the original?
>>>
>>> The solution we came up with was to create a third array type, T[new],
>>> which was a reference type.
>>>
>>> Andrei had the idea that T[new] could be dispensed with by making a
>>> "builder" library type to handle creating arrays by doing things like
>>> appending, and then delivering a finished T[] type. This is similar to
>>> what std.outbuffer and std.array.Appender do, they just need a bit of
>>> refining.
>>>
>>> The .length property of T[] would then become an rvalue only, not an
>>> lvalue, and ~= would no longer be allowed for T[].
>>>
>>> We both feel that this would simplify D, make it more flexible, and
>>> remove some awkward corner cases like the inability to say a.length++.
>>>
>>> What do you think?
>> I think ArrayBuilder can work almost entirely transparently provided the
> following conditions are met:
>> 1) when trying to cat to an array, the first array automatically promotes to
> ArrayBuilder
>> 2) Setting .length is, depending on new length, either a slice or a cat
> operation with the length difference.
>> 2) ArrayBuilders implicitly cast to string.
>> This should allow a syntax that is almost entirely identical to the one used in
> D1, aside from typeof("a"~"b").stringof :)
>> Is this feasible in D2?
> 
> Once you throw in all the implicit conversions to ArrayBuilder and having the core
> language know about ArrayBuilder, aren't you, for all practical purposes,
> implementing T[new] but calling it ArrayBuilder?

Yes but changing the semantics of a library object is easier than changing the semantics of a language feature. Besides, I think the builder works differently internally than T[new], although I'm not sure - storing lists or trees of sub-arrays and concatenating them lazily? At least that's what I would do :p