Why set default reus to singleton when using WithMefAttributedModel rule?

[zplan]

I am using Mef Import attributes in some ctors like:

    public MyClass(
        IMyInterface myType,
        [Import("a")] IProvide<A> myA,
        [Import("ab")] IProvide<A> myAB)
    {
     ...

Therefore I enabled the rule

IContainer container = new Container(rules => rules
                .WithMefAttributedModel());

--> But then I suddenly had singletons everywhere! Also for my non-mef registrations.
When I checked the DryIoC implementation of the rule I have seen in AttributedModel.cs:

        /// <summary>Adjusts the rules to provide the full MEF compatibility.</summary>
        public static Rules WithMefRules(this Rules rules)
        {
            var importMadeOf = rules.FactoryMethodOrSelector == null ? _defaultImportMadeOf :
                Made.Of(request => GetImportingConstructor(request, rules.FactoryMethodOrSelector),
                    GetImportedParameter, _getImportedPropertiesAndFields);

            return rules.With(importMadeOf)
                .WithDefaultReuse(Reuse.Singleton)
                .WithTrackingDisposableTransients();
        }

Why is the rule setting the default reuse to Singleton (second last line)?

[dadhi]

Hi @zplan.

It set so because [PartCreationPolicy(CreationPolicy.Shared)] is the default in MEF.

Regarding non-MEF registrations - there is no distinction for them when they are already in the container registry.

There was an alternative to set Reuse.Singleton for the specific MEF registration,
but then you lose the ability to override the registration with the container rules. So there are pros and cons.