Method parameter: Interface VS Generic type

Question

What are the arguments to use one or another of those two method implementations (in Example class)?

public interface IInterface { void DoIt(); } public class Example { public void MethodInterface(IInterface arg) { arg.DoIt(); } public void MethodGeneric<T>(T arg) where T: IInterface { arg.DoIt(); } }

PS: If method returns an IInterface or T I would choose the "generic" way to avoid further casting in type T if needed.

I didn't understand your question. Are you asking about which practice is better? — Saeed Neamati
– Saeed Neamati, Commented Nov 13, 2013 at 10:01
I don’t think it makes a real difference in this case, but I would argue that using generics here is unnecessarily complicating the situation and likely adds an overhead to the function definition. — poke
– poke, Commented Nov 13, 2013 at 10:02
@Saeed Neamati: yes best practice but most of all, impacts on design, compilation, further issue we may encounter with one or the other way or maybe one of those solutions is terribly wrong for some reason I am not able to spot. — Askolein
– Askolein, Commented Nov 13, 2013 at 10:05

Sriram Sakthivel · Accepted Answer · 2013-11-13 10:09:05Z

Both appears to be same, but really not.

Generic version will not box the ValueType when passed where as non generic version requires "boxing"

Here is a small sample program and relevant IL which demonstrates the situation

void Main() { Example ex = new Example(); TestStruct tex = new TestStruct(); ex.MethodGeneric(tex); ex.MethodInterface(tex); } public interface IInterface { void DoIt(); } public class Example { public void MethodInterface(IInterface arg) { arg.DoIt(); } public void MethodGeneric<T>(T arg) where T : IInterface { arg.DoIt(); } } internal struct TestStruct : IInterface { public void DoIt() { } }

Below is the relevant part of IL generated

IL_0001: newobj UserQuery+Example..ctor IL_0006: stloc.0 // ex IL_0007: ldloca.s 01 // tex IL_0009: initobj UserQuery.TestStruct IL_000F: ldloc.0 // ex IL_0010: ldloc.1 // tex IL_0011: callvirt UserQuery+Example.MethodGeneric IL_0016: nop IL_0017: ldloc.0 // ex IL_0018: ldloc.1 // tex IL_0019: box UserQuery.TestStruct //<--Box opcode IL_001E: callvirt UserQuery+Example.MethodInterface

Though it is a matter of preference, While MethodGeneric is the one which will perform better in case of "ValueTypes"

Saeed Neamati · Accepted Answer · 2013-11-13 10:15:14Z

I suggest passing Interface as a simple parameter, instead of using generic approach, for these reasons:

Simpler design, which results in better maintainability
More readable code, lesser professional knowledge
Better support for Dependency Injection and IoC
No reflection (I'm not sure about this, I'm going to provide proof, because generics use reflection to understand the type)

The interface is used in either case so this answer is ambiguous.

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