Type.GetGenericParameterConstraints メソッド

.NET Framework クラス ライブラリ リファレンス

Type.GetGenericParameterConstraints メソッド

メモ : このメソッドは、.NET Framework version 2.0 で新しく追加されたものです。

現在のジェネリック型パラメータの制約を表す Type オブジェクトを返します。

名前空間: System
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

Public Overridable Function
 GetGenericParameterConstraints As Type()

Visual Basic (使用法)

Dim instance As Type
Dim returnValue As Type()

returnValue = instance.GetGenericParameterConstraints

C#

public virtual Type[] GetGenericParameterConstraints ()

C++

public:
virtual array<Type^>^ GetGenericParameterConstraints ()

J#

public Type[] GetGenericParameterConstraints ()

JScript

public function GetGenericParameterConstraints
 () : Type[]

戻り値
現在のジェネリック型パラメータの制約を表す Type の配列。

例外

例外の種類	条件
InvalidOperationException	現在の Type オブジェクトは、ジェネリック型パラメータではありません。つまり、IsGenericParameter プロパティは false を返します。

解説

ジェネリック型パラメータの各制約は、Type オブジェクトとして表されます。IsClass プロパティを使用して、制約が基本クラスの制約であるかどうかを判断します。プロパティが false を返した場合、制約はインターフェイス制約です。型パラメータにクラス制約やインターフェイス制約がない場合は、空の配列が返されます。

ジェネリック リフレクションで使用される用語の一定の条件の一覧については、IsGenericType のプロパティの解説を参照してください。

使用例

異なる制約を持つ 2 つの型パラメータを指定したジェネリック型 Test を定義するコード例を次に示します。プログラムを実行すると、GenericParameterAttributes プロパティおよび GetGenericParameterConstraints メソッドを使って制約が調べられます。

Visual Basic

Imports System
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
' 

C#

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
 */

C++

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
 */

プラットフォーム

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

開発プラットフォームの中には、.NET Framework によってサポートされていないバージョンがあります。サポートされているバージョンについては、「システム要件」を参照してください。

バージョン情報

.NET Framework
サポート対象 : 2.0

参照

関連項目
Type クラス
Type メンバ
System 名前空間
GenericParameterAttributes
IsGenericParameter
その他の技術情報
方法 : リフレクションを使用してジェネリック型をチェックおよびインスタンス化する