Question

为什么我无法将None添加到System.Collections.Generic.Dictionary的{{1}}？这是Mono中的预期行为还是错误？

Option

我在OS X上使用Mono。

F# Interactive for F# 3.1 (Open Source Edition)
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> open System.Collections.Generic;;
> let d1 = new Dictionary<int option, int>();;

val d1 : Dictionary<int option,int> = dict []

> d1.Add(None, 1);;
System.ArgumentNullException: Value cannot be null.
Parameter name: key
   at System.ThrowHelper.ThrowArgumentNullException (ExceptionArgument argument) in <filename unknown>:line 0
   at System.Collections.Generic.Dictionary`2[TKey,TValue].Insert (System.Collections.Generic.TKey key, System.Collections.Generic.TValue value, Boolean add) in <filename unknown>:line 0
   at System.Collections.Generic.Dictionary`2[TKey,TValue].Add (System.Collections.Generic.TKey key, System.Collections.Generic.TValue value) in <filename unknown>:line 0
   at <StartupCode$FSI_0004>.$FSI_0004.main@ () in <filename unknown>:line 0
   at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
   at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) in <filename unknown>:line 0
Stopped due to error
> d1.Add(Some 10, 1);;
val it : unit = ()

Answer 1

它不是一个错误。选项＆LT;＆＃39; T＆GT;使用属性[CompilationRepresentation（CompilationRepresentationFlags.UseNullAsTrueValue)）导致None被表示为null。

所以你实际上是在为一个字典添加一个null作为你知道不允许的字典。

供参考：

UseNullAsTrueValue：允许使用null作为歧视联盟中的否定鉴别器的表示。

此处提供更多信息Why is None represented as null?

F＃选项词典

1 个答案: