GenericParameterAttributes 列挙体とは何？わかりやすく解説 Weblio辞書

.NET Framework クラスライブラリリファレンス

索引トップ用語の索引ランキング

GenericParameterAttributes 列挙体

メモ : この列挙体は、.NET Framework version 2.0 で新しく追加されたものです。

ジェネリック型またはジェネリックメソッドのジェネリック型パラメータに関する制約について説明します。

この列挙体には、メンバ値のビットごとの組み合わせを可能にする FlagsAttribute 属性が含まれています。

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

Visual Basic (宣言)

<FlagsAttribute> _
Public Enumeration GenericParameterAttributes

Visual Basic (使用法)

Dim instance As GenericParameterAttributes

[FlagsAttribute] 
public enum GenericParameterAttributes

C++

[FlagsAttribute] 
public enum class GenericParameterAttributes

/** @attribute FlagsAttribute() */ 
public enum GenericParameterAttributes

JScript

FlagsAttribute 
public enum GenericParameterAttributes

メンバ

	メンバ名	説明
	Contravariant	ジェネリック型パラメータが反変の型パラメータです。反変の型パラメータは、メソッドのシグネチャのパラメータ型として現れます。
	Covariant	ジェネリック型パラメータが共変の型パラメータです。共変の型パラメータは、メソッドの結果型、読み取り専用フィールドの型、宣言された基本型、または実装されたインターフェイスとして現れます。
	DefaultConstructorConstraint	型がパラメータなしのコンストラクタを持つ場合のみ、その型をジェネリック型パラメータの代わりに使用できます。
	None	特別なフラグはありません。
	NotNullableValueTypeConstraint	型が値型で null 許容でない場合のみ、その型をジェネリック型パラメータの代わりに使用できます。
	ReferenceTypeConstraint	型が参照型である場合のみ、その型をジェネリック型パラメータの代わりに使用できます。
	SpecialConstraintMask	すべての特殊な制約フラグの組み合わせを選択します。この値は、論理 OR を使用して DefaultConstructorConstraint フラグ、ReferenceTypeConstraint フラグ、および NotNullableValueTypeConstraint フラグを組み合わせた結果です。
	VarianceMask	すべての変性フラグの組み合わせを選択します。この値は、論理 OR を使用して Contravariant フラグと Covariant フラグを組み合わせた結果です。

解説

GenericParameterAttributes 列挙体のメンバは、変性グループおよび特殊な制約グループという、2 つのグループに分けられます。変性フラグの GenericParameterAttributes 値をテストするには、最初に VarianceMask を使用してビットごとの AND 演算を実行します。結果が None である場合、変性フラグはありません。同様に、制約フラグのテストには SpecialConstraintMask を使用します。

使用例

2 つの型パラメータを使用して Test というジェネリック型を定義するコード例を次に示します。2 つ目の型パラメータでは、基本クラスの制約と参照型の制約が指定されます。プログラムの実行時に、Type.GenericParameterAttributes プロパティと Type.GetGenericParameterConstraints メソッドを使用して制約がチェックされます。

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
'

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
 */