On Sun, 23 May 2010 17:36:52 -0400, Andrei Alexandrescu
<[email protected]> 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; }
...
}
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.
Yes, but most containers are node-based, so as long as you use structs for
nodes, you are generally in control of the bulk of allocation
(dcollections does this).
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.
Classes have builtin object monitors. But you could handle that via a
struct as well. The language support wouldn't be there though.
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.
The thing that classes really give you is the language support. Structs
need to be hand-crafted to support the same syntax. Classes are enforced
as always being reference types and always being on the heap. The
Value!(C) is questionable because creating the head of a container on the
stack leads to easily escaped stack references.
But yeah, a struct as a 'smart pointer' could work, as long as you don't
'auto-create' like AA's do.
It seems Steve took the weekend off.
My son's 2nd birthday party was Saturday, and I had visitors, sorry :) I
did some responses, but at some point if you want to remain married, you
have to pay attention to your family.
-Steve
