How to Accurately Select Generic Methods with Reflection at Compile Time?

Use reflection to select generic methods

Reflection allows calling methods with specific generic type parameters, but when multiple generic overloads are present, choosing the appropriate method can be challenging. This article demonstrates a compile-time approach to precisely selecting a target generic method by manipulating delegate and method information objects.

Use delegate selection method

For static methods, creating a delegate with the required number of generics and parameters enables the selection of specific overloads. For example, to select the first overload of DoSomething<TModel>, it has only one generic parameter:

<code class="language-C#">var method = new Action<object>(MyClass.DoSomething<object>);</code>

or the second overload, which has two generic parameters:

<code class="language-C#">var method = new Action<object, object>(MyClass.DoSomething<object, object>);</code>

For static extension methods, follow a similar pattern, using the appropriate types to handle the this parameters:

<code class="language-C#">var method = new Func<IQueryable<object>, Expression<Func<bool>>, IQueryable<object>>(Queryable.Where<object>);</code>

Get method information

The

delegate's Method property provides the underlying MethodInfo object. To get a generic method definition and provide specific type parameters:

<code class="language-C#">var methodInfo = method.Method.MakeGenericMethod(type1, type2);</code>

Instance methods

To select an instance method, the process is similar:

<code class="language-C#">var method = new Action<object>(instance.MyMethod<object>);
var methodInfo = method.Method.GetGenericMethodDefinition().MakeGenericMethod(type1);</code>

Decoupling method selection and parameter types

If the generic type parameters are not determined until later:

<code class="language-C#">var methodInfo = method.Method.GetGenericMethodDefinition();</code>

Later, pass the desired type to MakeGenericMethod():

<code class="language-C#">methodInfo.MakeGenericMethod(type1, type2);</code>

Conclusion

This approach enables precise selection of generic methods at compile time, avoiding error-prone runtime searches or use of strings. It provides a robust and flexible mechanism for calling generic methods with various type parameters.

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