是否可以使用运算符？并抛出新的Exception（）？ [英] Is it possible to use operator ?? and throw new Exception()?

问题描述

接下来我有很多方法：

var result = command.ExecuteScalar() as Int32?;
if(result.HasValue)
{
   return result.Value;
}
else
{
   throw new Exception(); // just an example, in my code I throw my own exception
}

我希望我可以这样使用运算符 ?? ：

I wish I could use operator ?? like this:

return command.ExecuteScalar() as Int32? ?? throw new Exception();

但它会生成编译错误。

是否可以重写我的代码，或者只有一种方法可以做到这一点？

Is it possible to rewrite my code or there is only one way to do that?

推荐答案

对于C＃7

在C＃7中， throw 成为表达式，因此可以完全使用其中描述的代码问题。

In C# 7, throw becomes an expression, so it's fine to use exactly the code described in the question.

对于C＃6和更早版本

在C＃6和更早版本中直接 -??的第二个操作数

You can't do that directly in C# 6 and earlier - the second operand of ?? needs to be an expression, not a throw statement.

如果您实际上只是想找到一个简洁的选项，则有几种选择：

There are a few alternatives if you're really just trying to find an option which is concise:

您可以这样写：

public static T ThrowException<T>()
{
    throw new Exception(); // Could pass this in
}

然后：

return command.ExecuteScalar() as int? ?? ThrowException<int?>();

我真的不建议您这样做...

I really don't recommend that you do that though... it's pretty horrible and unidiomatic.

扩展方法怎么样：

public static T ThrowIfNull(this T value)
{
    if (value == null)
    {
        throw new Exception(); // Use a better exception of course
    }
    return value;
}

然后：

return (command.ExecuteScalar() as int?).ThrowIfNull();

还有另一种选择（同样是扩展方法）：

Yet another alternative (again an extension method):

public static T? CastOrThrow<T>(this object x) 
    where T : struct
{
    T? ret = x as T?;
    if (ret == null)
    {
        throw new Exception(); // Again, get a better exception
    }
    return ret;
}

致电：

return command.ExecuteScalar().CastOrThrow<int>();

有点丑陋，因为您不能指定 int？作为类型参数...

It's somewhat ugly because you can't specify int? as the type argument...

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