Re: [Boost-users] Re: [Foreach]TroubleiteratingoverBoost.MultiIndexcontainers

David Abrahams wrote:

"Peter Dimov" writes:

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David Abrahams wrote:

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ADL might not be the best customization solution.

You keep saying that, but I keep disagreeing. ADL is the best customization solution. Not flawless, just better than any of the alternatives.

I guess I haven't seen enough be definitively convinced one way or the other. I have heard stories from people who switch to dispatching via specialization and report how much better things get. Furthermore, Daveed Vandevoorde has convinced me that it is far easier to reason about. The rules for matching partial specializations are trivial compared to the mess you have to consider when there is overloading. The inconvenience of specialization is ugly, but it seems like a one-time cost that may be justified for what it buys us.

That's the thing. It doesn't actually buy us anything. It only claims to avoid potential problems. * Uglier syntax for defining a specialization. * Coupling; you need to include a primary template. * Does not allow a base-specific version to be picked up automatically for derived classes. * Does not allow non-exact matches. * If four libraries need the same operation, you need to specialize four primary templates. In practice people tend to respect de-facto standards; a + b is an addition, and swap(a, b) swaps a and b. The main fight is over who gets to keep the primary template. But this is not really a problem with ADL customization points, because in their purest form, there is no primary template. The primary template is usually a compatibility workaround for types that do not support the ADL interface yet.