Transforming a range back to the original type?

[Jakob Ovrum]

On Friday, 4 May 2012 at 13:22:47 UTC, Steven Schveighoffer wrote:
> Structs don't make very good containers.  A slice is not really 
> a container.

Most containers in std.container are structs. A struct can do 
everything a class can do, for example, you can choose whether to 
use reference semantics or not. So I don't think the assertion 
that structs aren't good for containers is true, when they can do 
so much more than classes. There is still debate whether 
std.container's containers should be classes or structs, but even 
so, third-party containers might have different requirements.

> What exactly are you looking for?  I mean, you want the 
> original type back, so you can reassign, is that all?  
> Something like this should work for that:
>
> c = makeContainer!typeof(c)(c.filter!(x => x < 3));
>
> Implementation left as an exercise.
>
> -Steve

It would obviously be a dead simple function, the question is 
whether it's generally useful enough for the standard library, 
which I personally don't see it being, at least not until I see 
at least one good example. I was just pointing out the fact that 
it would require a function to abstract away the construction for 
all reasonable containers T.

You would also have to decide on an explicit convention of 
construction when T is a user-defined type (e.g. define a 
constructor taking an input range), as such a function would 
effectively formalise it.

(By the way, the template instantiation shortcut syntax only 
works when the only argument has exactly one token; your example 
code has an error.)