nullable

Attribute value with a null reference assigned to a reference type or to a nullable value type.

属性值等同于分配给引用类型或分配给可为空值类型的空引用。

The result of an arithmetic operator is always nullable, even if the operands are nonnullable and ANSI_WARNINGS or ARITHABORT is set ON.

即使操作数不可为空并且ANSI_WARNINGS或ARITHABORT设置为ON，算术运算符的结果也始终可为空。

Operator defines the default value to be returned when a nullable type is assigned to a non-nullable type.

运算符定义当可空类型分配给非可空类型时返回的默认值。

A type parameter can be constrained to be a reference type, a non- nullable value type, and to have a default constructor .

类型参数可以约束为引用类型、不可为空值类型和具有默认构造函数。

Specifically, any type defined as Nullable(Of T) wasn't allowed to be optional.

特别地，定义为Nullable（OfT）的任何类型都不允许是可选的。

Use nullable types to represent things that exist or do not exist depending on the circumstance.

根据具体环境，使用可空类型来表示存在或不存在的事物。

The nullability property of arithmetic operators over floating point data type is always nullable.

对浮点数据类型执行运算的算术运算符的为空性属性始终可为空。

Assign a value to a nullable type just as you would for an ordinary value type, for example int?

为可以为null的类型赋值的方法与为一般值类型赋值的方法相同，如int？

In this case, define the field to be a nullable type instead of a value type.

在这种情况下，将该字段定义为可空类型而不是值类型。

Though most Rails developers do not like to keep constraints in the database, you should consider things like nullable columns.

虽然大多数Rails开发人员都不喜欢在数据库中保留限制，但您应该考虑像空列这样的事情。

The as operator must be used with a reference type or nullable type ('int' is a non-nullable value type).

as运算符必须与引用类型或可为null的类型一起使用（“int”是不可为null的值类型）。

You can declare variables and properties with nullable types, and you can declare an array with elements of a nullable type.

可以用可空类型来声明变量和属性，也可以用可空类型的元素来声明数组。

If there is no default value and the column is not nullable, the server will return an error and an exception will be thrown.

如果没有默认值且列不可为空值，服务器将返回错误，此时将引发异常。

You can also use the classes and methods of the System. Reflection namespace to generate Type objects that represent Nullable types.

还可以使用System.Reflection命名空间的类和方法来生成表示可以为null的类型的Type对象。

In the lower right part of the section, set all key columns of the output link to non-nullable by selecting No in the nullable column.

在本部分的右下侧，通过选择空列上的No可将所有输出链接的关键列都设置为非空。

Indicates whether the current Nullable object is equal to a specified object.

指示当前Nullable对象是否等于指定的对象。

Columns in the view select list can be nullable or not nullable.

视图选择列表中的列可以为空，也可以不为空。

You store a value in a variable or property of a nullable type in the normal way.

按常规方式将值存储在可空类型的变量或属性中。

Calling GetType on a Nullable type causes a boxing operation to be performed when the type is implicitly converted to Object.

如果对可空类型调用GetType，则在该类型被隐式转换为Object时将执行装箱操作。

True - then boxing takes place, but only the underlying type that the nullable object is based upon is boxed.

则会发生装箱过程，但只将可空对象所基于的基础类型装箱。