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I have a MethodInfo of a GenericMethodDefinition. Such as: CallMethod<T>(T arg, string arg2). The GetParameters() method will give me two ParameterInfo objects, the first of which is generic, the second of which is not. How can I get ParameterInfo to tell me it is generic? What about if it has constraints?
901
To examine a generic type and its type parametersGet an instance of Type that represents the generic type. In the following code, the type is obtained using the C# typeof operator ( GetType in Visual Basic, typeid in Visual C++). See the Type class topic for other ways to get a Type object.
From the point of view of reflection, the difference between a generic type and an ordinary type is that a generic type has associated with it a set of type parameters (if it is a generic type definition) or type arguments (if it is a constructed type). A generic method differs from an ordinary method in the same way.
Definition: “A generic type is a generic class or interface that is parameterized over types.” Essentially, generic types allow you to write a general, generic class (or method) that works with different types, allowing for code re-use.
The where clause in a generic definition specifies constraints on the types that are used as arguments for type parameters in a generic type, method, delegate, or local function. Constraints can specify interfaces, base classes, or require a generic type to be a reference, value, or unmanaged type.
Check ParameterType.IsGenericParameter.
You may also want to check ContainsGenericParameters, which will be true for something like MyMethod<T>(List<T> param). (Even though List<> isn't a generic parameter)
If IsGenericParameter is true, you can also call GetGenericParameterConstraints() to get interface or base type constraints, and you can check GenericParameterAttributes (a [Flags] enum) for new(), struct, or class constraints.
115
I think you are looking for these:
parameterInfo.ParameterType.ContainsGenericParameters
parameterInfo.ParameterType.GetGenericParameterConstraints()
In additional to others' answer to the second question: Yes we can get the constraints from ParameterInfo using GetGenericParameterConstraints(), but it doesn't work for all circumstances. Consider some generic method like this:
public static void MyMethod<T,V>() where T : Dictionary<int, int>
{
}
There is a constraint for this method, but the method doesn't have parameters(think about Enumerable.Cast). What I'm going to say is the constraint is not part of the parameters, but the method itself. We can get the constraints by:
method.GetGenericArguments()[0].BaseType //the constraint of T
method.GetGenericArguments()[1].BaseType //that of V: Object
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