Type.GetGenericParameterConstraints Метод

Определение

Пространство имен:

System

Сборки:

netstandard.dll, System.Runtime.dll

Исходный код:

Type.cs

Возвращает массив Type объектов, представляющих ограничения текущего параметра универсального типа.

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()

Возвращаемое значение

Type[]

Массив Type объектов, представляющих ограничения текущего параметра универсального типа.

Исключения

InvalidOperationException

Текущий Type объект не является параметром универсального типа. То есть IsGenericParameter свойство возвращается false.

Примеры

В следующем примере кода определяется универсальный тип Test с двумя параметрами типа, имеющими разные ограничения. При выполнении программы ограничения проверяются с помощью GenericParameterAttributes свойства и GetGenericParameterConstraints метода.

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
 */

open System
open System.Reflection

// Define a sample interface to use as an interface constraint.
type ITest = interface end

// Define a base type to use as a base class constraint.
type Base() = class end

// 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.
type Test<'T, 'U
    when 'T :> Base 
    and 'T :> ITest
    and 'U : not struct 
    and 'U : (new : unit -> 'U)>() = class end

// Define a type that derives from Base and implements ITest. This type
// satisfies the constraints on T in class Test.
type Derived() = 
    inherit Base()
    interface ITest

// List the variance and special constraint flags. 
let listGenericParameterAttributes (t: Type) =
    let gpa = t.GenericParameterAttributes
    let variance = gpa &&& GenericParameterAttributes.VarianceMask

    let mutable retval = 
        // Select the variance flags.
        if variance = GenericParameterAttributes.None then
            "No variance flag"
        else
            if variance &&& GenericParameterAttributes.Covariant |> int <> 0 then
                "Covariant"
            else
                "Contravariant"
    // Select 
    let constraints = gpa &&& GenericParameterAttributes.SpecialConstraintMask

    if constraints = GenericParameterAttributes.None then
        retval <- retval + " No special constraints"
    else
        if constraints &&& GenericParameterAttributes.ReferenceTypeConstraint |> int <> 0 then
            retval <- retval + " ReferenceTypeConstraint"
        if constraints &&& GenericParameterAttributes.NotNullableValueTypeConstraint |> int <> 0 then
            retval <- retval + " NotNullableValueTypeConstraint"
        if constraints &&& GenericParameterAttributes.DefaultConstructorConstraint |> int <> 0 then
            retval <- retval + " DefaultConstructorConstraint"
    retval


// To get the generic type definition, call .GetGenericTypeDefinition().
let def = typeof<Test<Derived, _>>.GetGenericTypeDefinition()
printfn $"\nExamining generic type {def}"

// Get the type parameters of the generic type definition,
// and display them.
let defparams = def.GetGenericArguments()
for tp in defparams do
    printfn $"\nType parameter: {tp.Name}"
    printfn $"\t{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.
    let tpConstraints = tp.GetGenericParameterConstraints()
    for tpc in tpConstraints do
        printfn $"\t{tpc}"

(* 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 для параметра универсального типа выражается как Type объект. IsClass Используйте свойство, чтобы определить, является ли ограничение ограничением базового класса; если свойство возвращаетсяfalse, ограничение является ограничением интерфейса. Если параметр типа не имеет ограничения класса и нет ограничений интерфейса, возвращается пустой массив.

Список инвариантных условий терминов, используемых в универсальном отражении, см. в IsGenericType примечаниях свойств.

См. также раздел

• GenericParameterAttributes
• IsGenericParameter
• Практическое руководство. Изучение и создание экземпляров универсальных типов с отражением