ASP.NET Core API 如何转换 ActionResult<T>到 T in action 方法 [英] How ASP.NET Core APIs convert ActionResult<T> to T in action methods
问题描述
以下面的代码为例,这是一个 API 操作:
As an example look at below code which is a an API action:
[HttpGet("send")]
public ActionResult<string> Send()
{
if (IsAuthorized())
{
return "Ok";
}
return Unauthorized(); // is of type UnauthorizedResult -> StatusCodeResult -> ActionResult -> IActionResult
}
我的问题是这里的数据转换是如何发生的?编译器怎么不失败?
My question is how this data conversion is happening here? How doesn't the compiler fail?
推荐答案
这是可能的,因为有一种称为运算符重载的语言特性,它允许创建自定义运算符.ActionResult 有这样一个实现:
This is possible due to a language feature called operator overloading which allows for the creation of custom operators. ActionResult has such an implementation:
public sealed class ActionResult<TValue> : IConvertToActionResult
{
public TValue Value { get; }
public ActionResult(TValue value)
{
/* error checking code removed */
Value = value;
}
public static implicit operator ActionResult<TValue>(TValue value)
{
return new ActionResult<TValue>(value);
}
}
public static 隐式运算符
即此方法为 TValue
提供逻辑,以隐式强制转换为类型 ActionResult.这是一个非常简单的方法,它创建一个新的 ActionResult
,并将值设置为一个名为 Value
的公共变量.这种方法使这合法:
public static implicit operator
I.e. this method provides the logic for TValue
to be implicitly casted to type ActionResult. It's a very simple method that creates a new ActionResult
with the value set to a public variable called Value
. This method makes this legal:
ActionResult<int> result = 10; <-- // same as new ActionResult(10)
这实际上为您在 Action 方法中所做的合法操作创建了语法糖.
This essentially creates syntatic sugar for what you do in the Action methods to be legal.
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