Friday, July 5, 2013

single-method interface ^ lambda

(In this discussion I suppose it's probably OK to ignore the multicast feature of delegates.)

update -- see java lambda and "functional interface" on http://www.oracle.com/technetwork/articles/java/lambda-1984522.html

I used to feel a (unicast) delegate TYPE is quite similar to a single-method interface. Now I doubt it.

C++ has abstract classes. When all the methods are pure virtual, that's an interface (as in java). In this tradition, an interface is typically implemented by a Stateful class. Most textbooks and most schools introduce interface of this kind. What if the implementation class is stateless?

(To keep things simple let's suppose there's just 1 method.)  Then the objects used to implement the method must be passed in. This feels like a static utility method without the static keyword. Such an interface is quite a different animal from the traditional interface. Lambda is the best example. But also
- static nested classes in java
- anonymous delegates

Where c# API uses a lambda, java often uses a functional interface (i.e. single-method interface), since Java didn't support lambda until Java 8.

I feel in both c# and c++, lambda is often used as a function argument (not "parameter"). Imagine you have a method parameter whose
type is an SMI,
- and this interface has just 1 (or few) implementation(s)
- and the instance of this implementation class is basically stateless,

then this SMI parameter is probably a lambda trapped in an SMI. C# 3.0 and c++11 would liberate it.

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