比较两个可空值
Comparing two null nullables
C# 5.0 规范在第 7.1.3 章中读取
https://msdn.microsoft.com/en-us/library/ms228593.aspx
The lifted operator produces the value false if one or both operands are null.
但是测试以及这个 MSDN link
http://msdn.microsoft.com/en-us/library/2cf62fcy(v=vs.100).aspx
int? num1 = 10;
int? num2 = null;
// Change the value of num1, so that both num1 and num2 are null.
num1 = null;
if (num1 == num2)
{
// The equality comparison returns true when both operands are null.
Console.WriteLine("num1 == num2 returns true when the value of each is null");
}
/* Output:
* num1 == num2 returns true when the value of each is null
*/
显示比较两个可为 null returns true.
的可为空值
说得有道理，但与规范中的句子相矛盾，不是吗？
规范后来说
• For the equality operators
== != a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool. The
lifted form is constructed by adding a single ? modifier to each
operand type. The lifted operator considers two null values equal, and
a null value unequal to any non-null value. If both operands are
non-null, the lifted operator unwraps the operands and applies the
underlying operator to produce the bool result.
不要混用，这是关于不同类型的运算符。
• For the equality operators
== !=
a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool. The lifted form is constructed by adding a single ? modifier to each operand type. The lifted operator considers two null values equal, and a null value unequal to any non-null value. If both operands are non-null, the lifted operator unwraps the operands and applies the underlying operator to produce the bool result.
• For the relational operators
< > <= >=
a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool. The lifted form is constructed by adding a single ? modifier to each operand type. The lifted operator produces the value false if one or both operands are null. Otherwise, the lifted operator unwraps the operands and applies the underlying operator to produce the bool result.
C# 5.0 规范在第 7.1.3 章中读取
https://msdn.microsoft.com/en-us/library/ms228593.aspx
The lifted operator produces the value
falseif one or both operands arenull.
但是测试以及这个 MSDN link
http://msdn.microsoft.com/en-us/library/2cf62fcy(v=vs.100).aspx
int? num1 = 10;
int? num2 = null;
// Change the value of num1, so that both num1 and num2 are null.
num1 = null;
if (num1 == num2)
{
// The equality comparison returns true when both operands are null.
Console.WriteLine("num1 == num2 returns true when the value of each is null");
}
/* Output:
* num1 == num2 returns true when the value of each is null
*/
显示比较两个可为 null returns true.
说得有道理，但与规范中的句子相矛盾，不是吗？
规范后来说
• For the equality operators == != a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool. The lifted form is constructed by adding a single ? modifier to each operand type. The lifted operator considers two null values equal, and a null value unequal to any non-null value. If both operands are non-null, the lifted operator unwraps the operands and applies the underlying operator to produce the bool result.
不要混用，这是关于不同类型的运算符。
• For the equality operators == != a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool. The lifted form is constructed by adding a single ? modifier to each operand type. The lifted operator considers two null values equal, and a null value unequal to any non-null value. If both operands are non-null, the lifted operator unwraps the operands and applies the underlying operator to produce the bool result.
• For the relational operators < > <= >= a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool. The lifted form is constructed by adding a single ? modifier to each operand type. The lifted operator produces the value false if one or both operands are null. Otherwise, the lifted operator unwraps the operands and applies the underlying operator to produce the bool result.