27

I have some logic in a method that operates on a specified type and I'd like to create a generic lambda that encapsulates the logic. This is the spirit of what I'm trying to do:

public void DoSomething()
{
    // ...

    Func<T> GetTypeName = () => T.GetType().Name;

    GetTypeName<string>();
    GetTypeName<DateTime>();
    GetTypeName<int>();

    // ...
}

I know I can pass the type as a parameter or create a generic method. But I'm interested to know if a lambda can define its own generic parameters. (So I'm not looking for alternatives.) From what I can tell, C# 3.0 doesn't support this.

DavidRR
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hcoverlambda
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  • What are you trying to do, *exactly*? Remember that a lambda expression is just a function without a name, and the variable (Func or Action) is just a pointer (delegate) to that function . If you're more specific about your problem, maybe we can help better. – Robear Apr 07 '16 at 16:17

4 Answers4

30

While Jared Parson's answer is historically correct (2010!), this question is the first hit in Google if you search for "generic lambda C#". While there is no syntax for lambdas to accept additional generic arguments, you can now use local (generic) functions to achieve the same result. As they capture context, they're pretty much what you're looking for.

public void DoSomething()
{
    // ...

    string GetTypeName<T>() => typeof(T).GetType().Name;

    string nameOfString = GetTypeName<string>();
    string nameOfDT = GetTypeName<DateTime>();
    string nameOfInt = GetTypeName<int>();

    // ...
}
DavidRR
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ZaldronGG
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    I fixed your example so that it will compile and made it clear that the defined local generic function returns a string. Hope you find my changes acceptable. I learned something new from your example! Unfortunately, in the C# Programming Guide, the topic [Local functions](https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/local-functions) (added in C# 7.0) doesn't say anything about support for generic parameters. – DavidRR Feb 07 '19 at 16:09
18

It is not possible to create a lambda expression which has new generic parameters. You can re-use generic parameters on the containing methods or types but not create new ones.

JaredPar
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1

While you cannot (yet?) have a generic lambda (see also this answer and one comment to this question), you can get the same usage syntax. If you define:

public static class TypeNameGetter
{
    public static string GetTypeName<T>()
    {
        return typeof( T ).Name;
    }
}

The you can use it (though using static is C# 6) as:

using static TypeNameGetter;
public class Test
{
    public void Test1()
    {
        var s1 = GetTypeName<int>();
        var s2 = GetTypeName<string>();
    }
}
Pablo H
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0

This is only possible when your DoSomething method is generic or its class is generic.

Steven
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