[英]Why does dynamic.ToString() return something between a string and not a string?
I use a type derived from a DynamicObject
as a builder for some strings. 我使用从
DynamicObject
派生的类型作为某些字符串的构建器。 At the end I call ToString
to get the final result. 最后,我调用
ToString
来获得最终结果。
At this point I thought it would give me a normal string but this string is somehow strange. 在这一点上,我认为它会给我一个正常的字符串,但这个字符串有点奇怪。 It behaves like one when I use string functions on it but it behaves like I don't know actually what, something neither a string nor a dynamic.
当我在其上使用字符串函数时,它的行为就像一个,但它的行为就像我实际上不知道什么,既不是字符串也不是动态。
This is how I implemented ToString
on my builder 这就是我在构建器上实现
ToString
public class Example : DynamicObject
{
public override bool TryConvert(ConvertBinder binder, out object result)
{
if (binder.ReturnType == typeof(string))
{
result = ToString();
return true;
}
result = null;
return false;
}
public override string ToString()
{
return base.ToString();
}
}
When I run it like this 当我像这样运行它
dynamic example = new Example();
Console.WriteLine(example.ToString().ToUpper());
the result is correct: USERQUERY+EXAMPLE
(when executed in LINQPad) 结果是正确的:
USERQUERY+EXAMPLE
(在LINQPad中执行时)
However if I call the second line like this 但是,如果我像这样打电话给第二行
Console.WriteLine(example.ToString().Extension());
where 哪里
static class Extensions
{
public static string Extension(this string str)
{
return str.ToUpper();
}
}
the application crashes with a RuntimeBinderException
saying 应用程序崩溃与
RuntimeBinderException
说
'string' does not contain a definition for 'Extension'
'string'不包含'Extension'的定义
but if I cast the result it works again 但如果我把结果再次投入使用
Console.WriteLine(((string)example.ToString()).Extension());
Maybe one more example. 也许还有一个例子。
Console.WriteLine((string)example); // UserQuery+Example
but 但
Console.WriteLine(example); // DynamicObject UserQuery+Example
You can actually never be sure what you'll get until you cast it to string. 实际上,在将其转换为字符串之前,您永远无法确定您将获得什么。
Why is this happening and is there a way to avoid the additional cast and get somehow a real string? 为什么会发生这种情况,有没有办法避免额外的演员表,并以某种方式获得真正的字符串?
That's because ToString
called on dynamic
is typed to return dynamic
and not string
: 那是因为调用
dynamic
的ToString
是为了返回dynamic
而不是string
:
dynamic example = new Example();
// test will be typed as dynamic
var test = example.ToString();
When you call ToUpper
on test
it will use dynamic binding and resolve to string.ToUpper
at runtime. 当您在
test
时调用ToUpper
时,它将使用动态绑定并在运行时解析为string.ToUpper
。 You have to cast to a concrete type to escape dynamic typing. 您必须转换为具体类型以逃避动态类型。
Extension methods is a compile-time feature and as such is not supported by dynamic
typing as extension method . 扩展方法是编译时功能,因此
dynamic
类型不支持扩展方法 。 You can still call it using regular static method invocation syntax. 您仍然可以使用常规静态方法调用语法来调用它。
Extensions.Extension(example.ToString());
But again - example.ToString()
will return dynamic
and type binding will happen at runtime to check if it can be used as a parameter to Extensions.Extension
call. 但是再次 -
example.ToString()
将返回dynamic
并且类型绑定将在运行时发生,以检查它是否可以用作Extensions.Extension
调用的参数。 Check this answer for details. 请查看此答案以获取详细信
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