How Can I Safely Select the Correct Generic Method Overload Using Reflection?

Use reflection to choose the appropriate generic method

Introduction

Selecting an appropriate generic method via reflection can be challenging, especially when there are multiple generic overloads of the method. This article explores a compile-safe and efficient way to select the correct generic method without relying on strings or runtime searches.

Efficient method selection

Using a lambda expression or delegate with a MethodInfo.MakeGenericMethod method allows specific generic overloads to be selected at compile time. For example, if you have the following generic method:

<code>public static void DoSomething<TModel>(TModel model)</code>

You can create a delegate to match its generic count and argument count:

<code>var method = new Action<object>(MyClass.DoSomething<object>);</code>

By replacing a generic type with object you can choose the correct overload without resorting to runtime pipes or risky string manipulation.

Static method

For static methods (such as those in the System.Linq.Queryable class) you can use a similar approach. For example, to select a IQueryable<TModel> method that takes Expression<Func<TModel, bool>> and Where, you would do the following:

<code>var method = new Func<IQueryable<object>, Expression<Func<object, bool>>, IQueryable<object>>(Queryable.Where<object>);</code>

Instance methods

To select an instance method, you can follow a similar pattern but use MakeGenericMethod to get the generic GetGenericMethodDefinition before calling MethodInfo.

Decoupling MethodInfo and parameter types

You can use GetGenericMethodDefinition to decouple the selection of MethodInfo from the assignment of the generic type, and pass the MethodInfo to another method that knows the type to be instantiated and calls the method with that type.

Real world examples

To illustrate this approach, consider a class with multiple overloads of a generic method CopyList . The following code shows how to select the correct overload using the above technique:

<code>var listTo = ReflectionHelper.GetIEnumerableType(fromValue.GetType());

var fn = new Func<IEnumerable<object>, Func<PropertyInfo, bool>, Dictionary<Type, Type>, IEnumerable<object>>(ModelTransform.CopyList<object>);

var copyListMethod = fn.GetMethodInfo().GetGenericMethodDefinition().MakeGenericMethod(listTo);

copyListMethod.Invoke(null, new object[] { fromValue, whereProps, typeMap });</code>

Conclusion

By leveraging the power of lambda expressions and delegates, you can elegantly select the correct generic method via reflection, ensuring compile-time safety and avoiding the pitfalls of string-based or runtime searches.

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