Expression.Default(Type) 方法

定義

命名空間:

System.Linq.Expressions

組件:

System.Linq.Expressions.dll

來源:

DefaultExpression.cs

建立 DefaultExpression，其 Type 屬性設定為指定的類型。

public:
 static System::Linq::Expressions::DefaultExpression ^ Default(Type ^ type);

public static System.Linq.Expressions.DefaultExpression Default (Type type);

static member Default : Type -> System.Linq.Expressions.DefaultExpression

Public Shared Function Default (type As Type) As DefaultExpression

參數

type

Type

要將 Type 屬性設定為與之相等的 Type。

傳回

DefaultExpression

DefaultExpression，其 NodeType 屬性等於 Default，而 Type 屬性設定為指定的類型。

範例

下列程式代碼範例示範如何建立代表指定型別預設值的表達式。

// Add the following directive to your file:
// using System.Linq.Expressions;

// This expression represents the default value of a type
// (0 for integer, null for a string, etc.)
Expression defaultExpr = Expression.Default(
                            typeof(byte)
                        );

// Print out the expression.
Console.WriteLine(defaultExpr.ToString());

// The following statement first creates an expression tree,
// then compiles it, and then executes it.
Console.WriteLine(
    Expression.Lambda<Func<byte>>(defaultExpr).Compile()());

// This code example produces the following output:
//
// default(Byte)
// 0

' Add the following directive to your file:
' Imports System.Linq.Expressions  

' This expression represents the default value of a type
' (0 for integer, null for a string, and so on).
Dim defaultExpr As Expression = Expression.Default(
                                        GetType(Byte)
                                    )

' Print the expression.
Console.WriteLine(defaultExpr.ToString())

' The following statement first creates an expression tree,
' then compiles it, and then executes it.
Console.WriteLine(
    Expression.Lambda(Of Func(Of Byte))(defaultExpr).Compile()())

' This code example produces the following output:
'
' default(Byte)
' 0