GenArgs is used to represent a generic argument list:
| GenArgs ::= |
|---|
Type [ ',' Type ]* |
We say that a type is closed if it contains no generic parameters; otherwise, it is open.
A given generic type definition can be instantiated with generic arguments to produce an instantiated type.
[Example: Given suitable definitions for the generic class MyList and value type Pair, we could instantiate them as follows:
newobj instance void class MyList`1<int32>::.ctor()
initobj valuetype Pair`2<int32, valuetype Pair<string,int32>>
end example]
[Example:
ldtoken !0 // !0 = generic parameter 0 in generic type definition
castclass class List`1<!1> // !1 = generic parameter 1 in generic type definition
box !!1 // !!1 = generic parameter 1 in generic method definition
end example]
The number of generic arguments in an instantiation shall match the number of generic parameters specified in the type or method definition.
The CLI does not support partial instantiation of generic types. And generic types shall not appear uninstantiated anywhere in metadata signature blobs.
The following kinds of type cannot be used as arguments in instantiations (of generic types or methods):
-
Byref types (e.g.,
System.Generic.Collection.List`1<string&>is invalid) -
Byref-like types, i.e. value types that contain fields that can point into the CIL evaluation stack (e.g.,
List<System.RuntimeArgumentHandle>is invalid) -
Typed references (e.g.
List<System.TypedReference>is invalid) -
Unmanaged pointers (e.g.
List<int32*>is invalid) -
void(e.g.,List<System.Void>is invalid)
[Rationale: Byrefs types cannot be used as generic arguments because some, indeed most, instantiations would be invalid. For example, since byrefs are not allowed as field types or as method return types, in the definition of List`1<string&>, one could not declare a field of type !0, nor a method that returned a type of !0. end rationale]
[Rationale: Unmanaged pointers are disallowed because as currently specified unmanaged pointers are not technically subclasses of System.Object. This restriction can be lifted, but currently the runtime enforces this restriction and this spec reflects that.]
Objects of instantiated types shall carry sufficient information to recover at runtime their exact type (including the types and number of their generic arguments). [Rationale: This is required to correctly implement casting and instance-of testing, as well as in reflection capabilities (System.Object::GetType). end rationale]