Decision on container design

[Tomek Sowiński]

Michel Fortin napisał:

> > Is there anything implementation specific in the outer struct that provides
> > ref semantics to Impl? If not, Container could be generic, parametrized by
> > Impl type.  
> 
> You could provide an implementation-specific version of some functions 
> as an optimization. For instance there is no need to create the Impl 
> when asking for the length, if the pointer is null, length is zero. 
> Typically, const function can be implemented in the outward container 
> with a shortcut checking for null.

I think the reference struct can still be orthogonal to the container.

	struct Ref(Impl)
	{
		private Impl* _impl;
		ref Impl impl() @property
		{
			if (!impl) impl = new Impl;
			return *impl;
		}

		static if (hasLength!Impl)
		{
			auto length() @property
			{
				return impl ? impl.length : 0;
			}
		}

		alias impl this;
	}

Reusability lightens the burden of the container's author (less fuss for user implementations) and somewhat standardizes containers as they all must exhibit a certain API with certain semantics to be able to fit into Ref.

The downside is that the syntax for the most common case (ref semantics) is a little nosier than for value-like behavior.

-- 
Tomek