How Can I Use a Variable's Type as a Generic Parameter in C#?

Using variable types as generic parameters in C#

Generics in C# provide compile-time type safety, requiring the type to be known at compile time.

Suppose you define a generic method:

bool DoesEntityExist<T>(Guid guid, ITransaction transaction) where T : IGloballyIdentifiable;

When you try to use it dynamically, you will encounter a compilation error:

Type t = entity.GetType();
DoesEntityExist<t>(entityGuid, transaction);

This is because t is only known at runtime, which violates the compile-time type safety principle of generics.

You can use reflection to handle dynamically typed generic methods:

MethodInfo method = GetType().GetMethod("DoesEntityExist")
                             .MakeGenericMethod(new Type[] { t });
method.Invoke(this, new object[] { entityGuid, transaction });

However, this approach is not ideal due to its complexity and performance overhead.

A better solution is to make your calling method generic and pass the type parameter as a type parameter:

void MyMethod<T>(T entity, Guid guid, ITransaction transaction)
{
    DoesEntityExist<T>(guid, transaction);
}

This way, you can dynamically specify the type when calling MyMethod, avoiding the use of reflection while maintaining type safety.

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