c# - 在新开关 c# 8.0 中使用 lambda 函数返回值

Question

我想在我的代码中使用新开关，用于方法结果 make log 和 return IActionResult。

我尝试做这样的事情：

var response = (this._coreRepository.Write(value.Content, data.Id.ToString())); \\return bool
return response switch
{
   true => () =>
   {
      this._log.LogInformation("Write is complited");
      return Ok();
   },
   false => () =>
   {
      this._log.LogInformation("Error in writing");
      return BadRequest();
   },
   _     => () =>
   {
      throw new Exception("Unexpected error");
   }
};

但是编译器对我说cannot convert lambda expression to type 'IActionResult' because it is not a delegate type。

我该如何解决？

Answer 1

问题是您的 switch 表达式返回 alambda expression但包含方法期望IActionResult。要解决此问题，您应该重写 return 语句以立即调用 switch 表达式的结果：

var response = (this._coreRepository.Write(value.Content, data.Id.ToString()));

return (response switch
{
   // Here we cast lambda expression to Func<IActionResult> so that compiler
   // can define the type of the switch expression as Func<IActionResult>.
   true => (Func<IActionResult>) (() =>
   {
      this._log.LogInformation("Write is complited");
      return Ok();
   }),
   false => () =>
   {
      this._log.LogInformation("Error in writing");
      return BadRequest();
   },
   _     => () =>
   {
      throw new Exception("Unexpected error");
   }
})(); // () - here we invoke Func<IActionResult>, the result of the switch expression.

---

如果我是你，我会用下一种方式重写这段代码，使其更容易阅读：

var response = (this._coreRepository.Write(value.Content, data.Id.ToString()));

// Now additional braces or casts are not required.
Func<IActionResult> func = response switch
{
   true => () =>
   {
      this._log.LogInformation("Write is complited");
      return Ok();
   },
   false => () =>
   {
      this._log.LogInformation("Error in writing");
      return BadRequest();
   },
   _     => () =>
   {
      throw new Exception("Unexpected error");
   }
}

return func();