Type.GetGenericParameterConstraints Метод

Определение

Возвращает массив объектов Type, которые представляют ограничения, накладываемые на параметр текущего универсального типа.Returns an array of Type objects that represent the constraints on the current generic type parameter.

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()

Возвраты

Type[]

Массив объектов Type, которые представляют ограничения, накладываемые на параметр текущего универсального типа.An array of Type objects that represent the constraints on the current generic type parameter.

Исключения

Текущий объект Type не является параметром универсального типа.The current Type object is not a generic type parameter. То есть свойство IsGenericParameter возвращает значение false.That is, the IsGenericParameter property returns false.

Примеры

В следующем примере кода определяется универсальный тип Test с двумя параметрами типа, имеющими разные ограничения.The following code example defines a generic type Test with two type parameters that have different constraints. При выполнении программы ограничения проверяются с помощью GenericParameterAttributes свойства GetGenericParameterConstraints и метода.When the program executes, the constraints are examined using the GenericParameterAttributes property and the GetGenericParameterConstraints method.

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
' 

Комментарии

Каждое ограничение параметра универсального типа выражается как Type объект.Each constraint on a generic type parameter is expressed as a Type object. Используйте свойство, чтобы определить, является ли ограничение ограничением базового класса. Если свойство возвращает false, ограничение является ограничением интерфейса. IsClassUse the IsClass property to determine whether a constraint is the base class constraint; if the property returns false, the constraint is an interface constraint. Если параметр типа не имеет ограничений класса и не имеет ограничений интерфейса, возвращается пустой массив.If a type parameter has no class constraint and no interface constraints, an empty array is returned.

Список неизменяемых условий для терминов, используемых в отражении универсальных типов, см. в примечаниях к описанию свойства IsGenericType.For a list of the invariant conditions for terms used in generic reflection, see the IsGenericType property remarks.

Применяется к

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