Type.GenericParameterAttributes Property
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Gets a combination of GenericParameterAttributes flags that describe the covariance and special constraints of the current generic type parameter.
Assembly: mscorlib (in mscorlib.dll)
'Declaration Public Overridable ReadOnly Property GenericParameterAttributes As GenericParameterAttributes
Property Value
Type: System.Reflection.GenericParameterAttributesA bitwise combination of GenericParameterAttributes values that describes the covariance and special constraints of the current generic type parameter.
| Exception | Condition |
|---|---|
| InvalidOperationException | The current Type object is not a generic type parameter. That is, the IsGenericParameter property returns false. |
| NotSupportedException | The invoked method is not supported in the base class. |
The value of this property contains flags that describe whether the current generic type parameter is covariant, and flags that describe any special constraints. Use the GenericParameterAttributes.VarianceMask value to select the covariance flags, and use the GenericParameterAttributes.SpecialConstraintMask value to select the constraint flags.
For a list of the invariant conditions for terms used in generic reflection, see the IsGenericType property remarks.
The following code example defines a generic type Test with two type parameters that have different constraints. When the program executes, the constraints are examined using the GenericParameterAttributes property and the GetGenericParameterConstraints method.
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To run this example, see Building examples that have static TextBlock controls for Windows Phone 8. |
Imports System.Reflection ' Define a sample interface to use as an interface constraint. Public Interface ITest End Interface ' Define a base type to use as a base class constraint. Public Class Base End Class ' Define the generic type to examine. The first generic type parameter, ' T, derives from the class Base and implements ITest. This demonstrates ' a base class constraint and an interface constraint. The second generic ' type parameter, U, must be a reference type (Class) and must have a ' default constructor (New). This demonstrates special constraints. ' Public Class Test(Of T As {Base, ITest}, U As {New, Class}) End Class ' Define a type that derives from Base and implements ITtest. This type ' satisfies the constraints on T in class Test. Public Class Derived Inherits Base Implements ITest End Class Public Class Example Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock) ' To get the generic type definition, omit the type ' arguments but retain the comma to indicate the number ' of type arguments. ' Dim def As Type = GetType(Test(Of ,)) outputBlock.Text += String.Format(vbCrLf & "Examining generic type {0}", def) & vbCrLf ' Get the type parameters of the generic type definition, ' and display them. ' Dim defparams() As Type = def.GetGenericArguments() For Each tp As Type In defparams outputBlock.Text += String.Format(vbCrLf & "Type parameter: {0}", tp.Name) & vbCrLf outputBlock.Text &= vbTab & ListGenericParameterAttributes(tp) & vbCrLf ' List the base class and interface constraints. The ' constraints do not appear in any particular order. An ' empty array is returned if there are no constraints. ' Dim tpConstraints As Type() = _ tp.GetGenericParameterConstraints() For Each tpc As Type In tpConstraints outputBlock.Text &= vbTab & tpc.ToString() & vbCrLf Next tpc Next tp End Sub ' List the variance and special constraint flags. ' Private Shared Function ListGenericParameterAttributes(ByVal t As Type) As String Dim retval As String Dim gpa As GenericParameterAttributes = t.GenericParameterAttributes ' Select the variance flags. Dim variance As GenericParameterAttributes = _ gpa And GenericParameterAttributes.VarianceMask If variance = GenericParameterAttributes.None Then retval = "No variance flag;" Else If (variance And GenericParameterAttributes.Covariant) <> 0 Then retval = "Covariant;" Else retval = "Contravariant;" End If End If ' Select the constraint flags. Dim constraints As GenericParameterAttributes = _ gpa And GenericParameterAttributes.SpecialConstraintMask If constraints = GenericParameterAttributes.None Then retval &= " no special constraints." Else If (constraints And GenericParameterAttributes.ReferenceTypeConstraint) <> 0 Then retval &= " ReferenceTypeConstraint" End If If (constraints And GenericParameterAttributes.NotNullableValueTypeConstraint) <> 0 Then retval &= " NotNullableValueTypeConstraint" End If If (constraints And GenericParameterAttributes.DefaultConstructorConstraint) <> 0 Then retval &= " DefaultConstructorConstraint" End If End If Return retval End Function End Class ' This example produces the following output: ' 'Examining generic type Test`2[T,U] ' 'Type parameter: T ' No variance flag; no special constraints. ' Base ' ITest ' 'Type parameter: U ' No variance flag; ReferenceTypeConstraint DefaultConstructorConstraint '
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