Type.GetGenericParameterConstraints Methode
Definition
Wichtig
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Gibt ein Array von Type-Objekten zurück, die die Einschränkungen für den aktuellen generischen Typparameter darstellen.
public:
virtual cli::array <Type ^> ^ GetGenericParameterConstraints();public virtual Type[] GetGenericParameterConstraints ();abstract member GetGenericParameterConstraints : unit -> Type[]
override this.GetGenericParameterConstraints : unit -> Type[]Public Overridable Function GetGenericParameterConstraints () As Type()Gibt zurück
- Type[]
Ein Array von Type-Objekten, die die Einschränkungen für den aktuellen generischen Typparameter darstellen.
Ausnahmen
Das aktuelle Type-Objekt ist kein generischer Typparameter. Das bedeutet, dass die IsGenericParameter-Eigenschaft false zurückgibt.
Beispiele
Im folgenden Codebeispiel wird ein generischer Typ Test mit zwei Typparametern definiert, die unterschiedliche Einschränkungen haben. Wenn das Programm ausgeführt wird, werden die Einschränkungen mithilfe der GenericParameterAttributes -Eigenschaft und der -Methode GetGenericParameterConstraints untersucht.
using namespace System;
using namespace System::Collections;
using namespace System::Reflection;
// Define a sample interface to use as an interface constraint.
interface class ITest{};
// Define a base type to use as a class constraint.
public ref class Base{};
// 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. In the .NET
// Framework version 2.0, C++ has no way of expressing special constraints.
// See the C# example code.
//
generic <typename T, typename U>
where T : Base, ITest
ref class Test {};
// Define a type that derives from Base and implements interface
// ITest. This type satisfies the constraint on T in class Test.
public ref class Derived: public Base, public ITest {};
public ref class Example
{
public:
static void Main()
{
// Create a constructed type from Test<T,U>, and from it
// get the generic type definition.
//
Type^ def = Test::typeid;
Console::WriteLine( L"\r\nExamining generic type {0}", def );
// Get the type parameters of the generic type definition,
// and display them.
//
for each (Type^ tp in def->GetGenericArguments())
{
Console::WriteLine( L"\r\nType parameter: {0}", tp);
Console::WriteLine( L"\t{0}",
ListGenericParameterAttributes( tp ) );
// List the base class and interface constraints. The
// constraints do not appear in any particular order. If
// there are no class or interface constraints, an empty
// array is returned.
//
for each (Type^ constraint in tp->GetGenericParameterConstraints())
{
Console::WriteLine( L"\t{0}", constraint );
}
}
}
private:
// List the variance and special constraint flags.
//
static String^ ListGenericParameterAttributes( Type^ t )
{
String^ retval;
GenericParameterAttributes gpa = t->GenericParameterAttributes;
// Select the variance flag.
GenericParameterAttributes variance =
static_cast<GenericParameterAttributes>(
gpa & GenericParameterAttributes::VarianceMask );
if ( variance == GenericParameterAttributes::None )
retval = L"No variance flag;";
else
{
if ( (variance & GenericParameterAttributes::Covariant) !=
GenericParameterAttributes::None )
retval = L"Covariant;";
else
retval = L"Contravariant;";
}
// Select the special constraint flags.
GenericParameterAttributes constraints =
static_cast<GenericParameterAttributes>(
gpa & GenericParameterAttributes::SpecialConstraintMask);
if ( constraints == GenericParameterAttributes::None )
retval = String::Concat( retval, L" No special constraints" );
else
{
if ( (constraints & GenericParameterAttributes::ReferenceTypeConstraint) !=
GenericParameterAttributes::None )
retval = String::Concat( retval, L" ReferenceTypeConstraint" );
if ( (constraints & GenericParameterAttributes::NotNullableValueTypeConstraint) !=
GenericParameterAttributes::None )
retval = String::Concat( retval, L" NotNullableValueTypeConstraint" );
if ( (constraints & GenericParameterAttributes::DefaultConstructorConstraint) !=
GenericParameterAttributes::None )
retval = String::Concat( retval, L" DefaultConstructorConstraint" );
}
return retval;
}
};
int main()
{
Example::Main();
}
/* 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; No special constraints
*/
using System;
using System.Reflection;
// Define a sample interface to use as an interface constraint.
public interface ITest {}
// Define a base type to use as a base class constraint.
public class Base {}
// 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<T,U>
where T : Base, ITest
where U : class, new() {}
// Define a type that derives from Base and implements ITest. This type
// satisfies the constraints on T in class Test.
public class Derived : Base, ITest {}
public class Example
{
public static void Main()
{
// To get the generic type definition, omit the type
// arguments but retain the comma to indicate the number
// of type arguments.
//
Type def = typeof(Test<,>);
Console.WriteLine("\r\nExamining generic type {0}", def);
// Get the type parameters of the generic type definition,
// and display them.
//
Type[] defparams = def.GetGenericArguments();
foreach (Type tp in defparams)
{
Console.WriteLine("\r\nType parameter: {0}", tp.Name);
Console.WriteLine("\t{0}",
ListGenericParameterAttributes(tp));
// List the base class and interface constraints. The
// constraints are returned in no particular order. If
// there are no class or interface constraints, an empty
// array is returned.
//
Type[] tpConstraints = tp.GetGenericParameterConstraints();
foreach (Type tpc in tpConstraints)
{
Console.WriteLine("\t{0}", tpc);
}
}
}
// List the variance and special constraint flags.
//
private static string ListGenericParameterAttributes(Type t)
{
string retval;
GenericParameterAttributes gpa = t.GenericParameterAttributes;
GenericParameterAttributes variance = gpa &
GenericParameterAttributes.VarianceMask;
// Select the variance flags.
if (variance == GenericParameterAttributes.None)
{
retval = "No variance flag;";
}
else
{
if ((variance & GenericParameterAttributes.Covariant) != 0)
retval = "Covariant;";
else
retval = "Contravariant;";
}
// Select
GenericParameterAttributes constraints = gpa &
GenericParameterAttributes.SpecialConstraintMask;
if (constraints == GenericParameterAttributes.None)
{
retval += " No special constraints";
}
else
{
if ((constraints & GenericParameterAttributes.ReferenceTypeConstraint) != 0)
retval += " ReferenceTypeConstraint";
if ((constraints & GenericParameterAttributes.NotNullableValueTypeConstraint) != 0)
retval += " NotNullableValueTypeConstraint";
if ((constraints & GenericParameterAttributes.DefaultConstructorConstraint) != 0)
retval += " DefaultConstructorConstraint";
}
return retval;
}
}
/* 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
*/
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 Main()
' 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 ,))
Console.WriteLine(vbCrLf & "Examining generic type {0}", def)
' 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
Console.WriteLine(vbCrLf & "Type parameter: {0}", tp.Name)
Console.WriteLine(vbTab & ListGenericParameterAttributes(tp))
' 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
Console.WriteLine(vbTab & tpc.ToString())
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
'
Hinweise
Jede Einschränkung für einen generischen Typparameter wird als -Objekt Type ausgedrückt. Verwenden Sie die -Eigenschaft, um zu bestimmen, ob eine Einschränkung die Basisklasseneinschränkung ist. Wenn die Eigenschaft zurückgibt, ist IsClass false die Einschränkung eine Schnittstelleneinschränkung. Wenn ein Typparameter über keine Klasseneinschränkung und keine Schnittstelleneinschränkungen verfügt, wird ein leeres Array zurückgegeben.
Eine Liste der invarianten Bedingungen für Begriffe, für Begriffe, die für die Reflektion mit generischen Methoden verwendet werden, finden Sie in den Hinweisen zur Eigenschaft IsGenericType.