Creating generic method and using type parameter

Question

I have created this method which is an object factory:

public static T GetService<T>(T serviceInterface)
{
    if (serviceInterface.Equals(typeof(IMemberService)))
    {
        return (T)(object)new MemberService();
    }
    else if (serviceInterface.Equals(typeof(ILookupService)))
    {
        return (T)(object)new LookupService();
    }
    throw new ArgumentOutOfRangeException("No action is defined for service interface " + serviceInterface.Name);
}

Now, I would like to go further and eliminate the need for "serviceInterface" parameter, but my problem is - I don't know how to compare type parameter T to an interface: doing

T.Equals(typeof(ILookupService))

gives compiler error: 'T' is a 'type parameter', which is not valid in the given context.

Any ideas how could I compare a type parameter to an interface?

Thank you, Andrey

You can pick value from serviceInterface variable like this -> stackoverflow.com/a/44114122/1580548 — ddagsan
– ddagsan, Commented May 22, 2017 at 13:30

JaredPar · Accepted Answer · 2010-02-17 23:02:05Z

17

You can use typeof(T) to get a Type object back which could replace the use of serviceInterface

For example

public static T GetService<T>()
{
    Type serviceInterface = typeof(T);
    if (serviceInterface.Equals(typeof(IMemberService)))
    {
        return (T)(object)new MemberService();
    }
    else if (serviceInterface.Equals(typeof(ILookupService)))
    {
        return (T)(object)new LookupService();
    }
    throw new ArgumentOutOfRangeException("No action is defined for service interface " + serviceInterface.Name);
}

answered Feb 17, 2010 at 23:02

JaredPar

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10 Comments

Andrey Over a year ago

Damn, now I'm embarrassed! Soooo simple! Thanks a bunch Jared!

spender Over a year ago

Sure, but will it ever equal an interface? If T represents the type of a concrete object, surely it won't equal an interface.

spender Over a year ago

OK agreed, but it gets smellier by the second

spender Over a year ago

To me it seems like a misappropriation of generics to start your generic method with checks for particular types/interfaces

spender Over a year ago

Andrey, there's probably nothing wrong. I just find it an unusual use of generics when the method branches according to the supplied generic type. In this situation I'd simply create two non-generic methods of fixed type. I appreciate (from Jared's comments) that this may not suit your purposes.

|

Kevin Montrose · Accepted Answer · 2010-02-17 23:02:59Z

2

Use typeof(T).

So,

typeof(T).Equals(typeof(ILookupService))

answered Feb 17, 2010 at 23:02

Kevin Montrose

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Comments

spender · Accepted Answer · 2010-02-17 23:05:55Z

1

Could the is operator be applicable here?

answered Feb 17, 2010 at 23:05

spender

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1 Comment

jv42 Over a year ago

is applies to objects not classes, so no, it wouldn't provide the OP with a solution. It could maybe be used in his original design, but not when removing the parameter.

spender · Accepted Answer · 2010-02-17 23:14:38Z

1

if (typeof(IMemberService).IsAssignableFrom(typeof(T)))
{}
else if (typeof(ILookupService).IsAssignableFrom(typeof(T)))
{}

edited Feb 17, 2010 at 23:14

spender

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answered Feb 17, 2010 at 23:07

Asad

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2 Comments

fre0n Over a year ago

Combine this answer (IsAssignableFrom) with JaredPar's answer, and you'll have the complete solution.

Andrey Over a year ago

What's wrong with my original solution? I need to know if it the type passed matches exactly to the interface I compare to

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