The demise of T[new]

[Andrei Alexandrescu]

Denis Koroskin wrote:
> On Mon, 19 Oct 2009 01:05:39 +0400, Walter Bright 
> <newshound1 at digitalmars.com> 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?
> 
> Well, I personally don't feel much of a need for T[new], and I agree T[] 
> needs to be "fixed" the way you describe (i.e. make a shrink-only range 
> out of it).
> But I believe a change like this coupled with a demise of T[new] would 
> be way too restricting. Given a
> 
> T[] array;
> 
> What type would result of these operations be?
> 
> 1) auto x = array.dup;
> 2) auto y = array ~ array;
> 
> T[] is a view into someone else's container. But when you create a new 
> array (by dup'ing or concatenating), you get a fresh copy. It points to 
> a beginning of data sequence, and there is nothing wrong to expand it.
> 
> I believe it should be T[new]. A reference type, yes, a type that would 
> allow appending and would render Appender unnecessary.

That was the exact plan. I even have half a chapter written about it 
with nice figures and all, that I can make available. The problem was, 
it sucked. Returning a distinct type from .dup and ~ makes slices not 
closed over these operations, a source of complication, confusion, and 
bloating.

Andrei