How Can I Instantiate a Generic Type in C# with a Variable as the Type Parameter?

instantiate a C# generic type using variables as type parameters

In C#, it is often necessary to create instances of generic types based on dynamically determined type parameters. However, providing type parameter values ​​directly in the new keyword is not possible and results in the following error:

<code>'List<k>' is a 'Type' but is used like a 'Type'</k></code>

Solution

To overcome this limitation, reflection can be used to explicitly construct generic types:

1. Get the type of a generic class (for example, List<T>):

   <code class="language-C#">Type genericListType = typeof(List<>);</code>

2. Replace <T> with the desired type to get a concrete generic type:

   <code class="language-C#">Type specificListType = genericListType.MakeGenericType(typeof(double));</code>

3. Use reflection to create an instance of a specific generic type:

   <code class="language-C#">var list = Activator.CreateInstance(specificListType);</code>

With this approach, you can create instances of a generic type that use variable-driven type parameters.

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