struct vs. class containers (was: Re: dcollections 1.0 and 2.0a beta released)

[Jacob Carlborg]

On 2010-05-23 23.36, Andrei Alexandrescu wrote:
> I've thought for a very long time about the class vs. struct choice in a
> container, and I came to a startling conclusion: it (almost) doesn't
> matter. Could be either, and the tradeoffs involved are nonessential.
> Here they are:
>
> 1. Using a class makes implementing members easier because there's no
> need to do work through an additional member. With a struct, you need a
> pimpl approach. For example:
>
> struct Array {
> struct Impl {
> ...
> }
> Impl * impl;
> ...
> @property length() const { return impl->length; }
> ...
> }

Isn't that just what "alias this" and "opDispatch" are for ?

> 2. struct gives you more power in managing collection's own memory, as
> long as the collection doesn't escape item addresses or other addresses
> of internal handles. So all other things being equal, struct has a net
> advantage.
>
> 3. The creation syntaxes are different. For Phobos, I suggest adding a
> simple function make() to std.algorithm. make!T(a, b, c) returns a newly
> constructed object T by invoking the constructor with arguments a, b,
> and c. That way we can make client code virtually agnostic of the
> class/struct choice for a container.
>
> That's it. Otherwise, one could use either to build a container. Let me
> note that I have reached the conclusion that containers should be at
> best reference types, with a meta-constructor Value!(C) that takes a
> container C and makes it into a value type.
>
> This result is the end of a long journey. I am quite sure I have it
> right. If anything, I am amazed at how much dogma I had to unlearn
> before reaching it. And I'm glad I did - this is very D-like: I wasn't
> looking for a class-based solution, and I wasn't looking for a
> struct-based solution. I was only looking for the truth - and surprise,
> this slightly asymmetric duality came forth.
>
> It seems Steve took the weekend off. At this point I'm poised to prepare
> a list of items that would condition putting dcollections in phobos. But
> I'd rather have Steve (and everyone) acquire their own motivation from
> my arguments, instead of operating changes as a concession.
>
>
> Andrei


-- 
/Jacob Carlborg