Type.GetGenericParameterConstraints Yöntem

Tanım

Ad Alanı:

System

Bütünleştirilmiş Kodlar:

netstandard.dll, System.Runtime.dll

Kaynak:

Type.cs

Geçerli genel tür parametresindeki kısıtlamaları temsil eden bir nesne dizisi Type döndürür.

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()

Döndürülenler

Type[]

Geçerli genel tür parametresindeki kısıtlamaları temsil eden bir nesne dizisi Type .

Özel durumlar

InvalidOperationException

Geçerli Type nesne genel bir tür parametresi değil. Yani özelliği IsGenericParameter döndürür false.

Örnekler

Aşağıdaki kod örneği, farklı kısıtlamaları olan iki tür parametresine sahip genel bir tür Test tanımlar. Program yürütürken, kısıtlamalar özelliği ve GenericParameterAttributes yöntemi kullanılarak GetGenericParameterConstraints incelenir.

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
'

Açıklamalar

Genel tür parametresindeki her kısıtlama bir Type nesne olarak ifade edilir. Bir kısıtlamanın IsClass temel sınıf kısıtlaması olup olmadığını belirlemek için özelliğini kullanın; özellik döndürürse false, kısıtlama bir arabirim kısıtlamasıdır. Tür parametresinde sınıf kısıtlaması yoksa ve arabirim kısıtlaması yoksa boş bir dizi döndürülür.

Genel yansımada kullanılan terimlere ilişkin sabit koşulların IsGenericType listesi için özellik açıklamalarına bakın.

Ayrıca bkz.

• GenericParameterAttributes
• IsGenericParameter
• Nasıl yapılır: Yansıma ile Genel Türleri İnceleme ve Örnekleme