奇怪的異常編譯動態構建的表達式

Question

我正在使用System.Ling.Expressions API創建和編譯一個表達式。編譯工作正常，但在某些情況下，當運行編譯的lambda時，我會遇到無法解釋的NullReferenceExceptions甚至是System.Security.Verification異常。作爲參考，此項目的目的是爲.NET類型創建和編譯自定義序列化器函數。

以下是對於debuginfo軟拋出一個NullReferenceException的表達式：

.Lambda #Lambda1<System.Action`2[IO.IWriter,<>f__AnonymousType1`2[System.Int32[],System.Int32]]>(
    IO.IWriter $writer, 
    <>f__AnonymousType1`2[System.Int32[],System.Int32] $t) { 
    .Block() { 
     .Invoke (.Lambda #Lambda2<System.Action`2[IO.IWriter,System.Int32[]]>)(
      $writer, 
      $t.a); 
     .Invoke (.Lambda #Lambda3<System.Action`2[IO.IWriter,System.Int32]>)(
      $writer, 
      $t.b) 
    } 
} 

.Lambda #Lambda2<System.Action`2[IO.IWriter,System.Int32[]]>(
    IO.IWriter $writer, 
    System.Int32[] $t) { 
    .Block() { 
     .Invoke (.Lambda #Lambda4<System.Action`2[IO.IWriter,System.Int32]>)(
      $writer, 
      .Call System.Linq.Enumerable.Count((System.Collections.Generic.IEnumerable`1[System.Int32])$t)); 
     .Call IO.SerializerHelpers.WriteCollectionElements(
      (System.Collections.Generic.IEnumerable`1[System.Int32])$t, 
      $writer, 
      .Lambda #Lambda3<System.Action`2[IO.IWriter,System.Int32]>) 
    } 
} 

.Lambda #Lambda3<System.Action`2[IO.IWriter,System.Int32]>(
    IO.IWriter $writer, 
    System.Int32 $t) { 
    .Call $writer.WriteInt($t) 
} 

.Lambda #Lambda4<System.Action`2[IO.IWriter,System.Int32]>(
    IO.IWriter $w, 
    System.Int32 $count) { 
    .Call $w.BeginWritingCollection($count) 
} 

異常被調用＃Lambda3，這是從WriteCollectionElements反覆調用中拋出。 WriteCollectionElements的實現如下：

static void WriteCollectionElements<T>(IEnumerable<T> collection, IWriter writer, Action<IWriter, T> writeAction) 
     { 
      foreach (var element in collection) 
      { 
       writeAction(writer, element); 
      } 
     } 

從這個函數內部調試，我已經確定，收集，作家的WriteAction和元素都是非空時，拋出異常。 ，我傳遞給編譯拉姆達的說法是：

new { a = new[] { 20, 10 }, b = 2 } 

而且奇怪的是，如果我刪除b屬性和重新生成我的串行功能，一切工作正常。在這種情況下，debuginfo軟的串行是：

.Lambda #Lambda1<System.Action`2[IO.IWriter,<>f__AnonymousType5`1[System.Int32[]]]>(
    IO.IWriter $writer, 
    <>f__AnonymousType5`1[System.Int32[]] $t) { 
    .Block() { 
     .Invoke (.Lambda #Lambda2<System.Action`2[IO.IWriter,System.Int32[]]>)(
      $writer, 
      $t.a) 
    } 
} 

.Lambda #Lambda2<System.Action`2[IO.IWriter,System.Int32[]]>(
    IO.IWriter $writer, 
    System.Int32[] $t) { 
    .Block() { 
     .Invoke (.Lambda #Lambda3<System.Action`2[IO.IWriter,System.Int32]>)(
      $writer, 
      .Call System.Linq.Enumerable.Count((System.Collections.Generic.IEnumerable`1[System.Int32])$t)); 
     .Call IO.SerializerHelpers.WriteCollectionElements(
      (System.Collections.Generic.IEnumerable`1[System.Int32])$t, 
      $writer, 
      .Lambda #Lambda4<System.Action`2[IO.IWriter,System.Int32]>) 
    } 
} 

.Lambda #Lambda3<System.Action`2[IO.IWriter,System.Int32]>(
    IO.IWriter $w, 
    System.Int32 $count) { 
    .Call $w.BeginWritingCollection($count) 
} 

.Lambda #Lambda4<System.Action`2[IO.IWriter,System.Int32]>(
    IO.IWriter $writer, 
    System.Int32 $t) { 
    .Call $writer.WriteInt($t) 
} 

我在Windows 7上運行.NET Framework 4（至少這是我的構建目標），VS快遞C＃2010

沒有人有任何想法什麼可能會出錯或嘗試調試的下一步？如果能提供幫助，我很樂意發佈更多信息。

編輯：我自從（據我所知）找到了解決這個bug的方法，儘管我沒有接近理解它爲什麼會發生。在生成我上面張貼的表達式的代碼，我有以下幾點：

MethodInfo writeCollectionElementsMethod = // the methodInfo for WriteCollectionElements with .MakeGenericMethod() called with typeof(T) 
Expression<Action<IWriter, T> writeActionExpression = // I created this expression separately 
ParameterExpression writerParameter, enumerableTParameter = // parameters of type IWriter and IEnumerable<T>, respectively 

// make an expression to invoke the method 
var methodCallExpression = Expression.Call(
    instance: null, // static 
    method: writeCollectionElementsMethod, 
    arguments: new[] { 
     enumerableTParameter, 
     writerParameter, 
     // passing in this expression correctly would produce the weird error in some cases as described above 
     writeActionExpression 
    } 
); 

// make an expression to invoke the method 
var methodCallExpressionV2 = Expression.Call(
    instance: null, // static 
    method: writeCollectionElementsMethod, 
    arguments: new[] { 
     enumerableTParameter, 
     writerParameter, 
     // this did not cause the bug 
     Expression.Constant(writeActionExpression.Compile()) 
    } 
); 

但是，我不喜歡單獨編制的每一個表情，所以我最終乾脆只用WriteCollectionElements功能做掉通過Expression.Loop，Expression.Break等動態創建foreach循環。

因此，我不再被阻止，但仍然非常好奇。

Answer 1

如果你建立手動在C＃ReSharper的抱怨在這種情況下，ReSharper的狀態在clousure

Action<IWriter, int> lambda4 = ((IWriter writer, int length) => writer.BeginWritingCollection(length)); 
Action<IWriter, int> lambda3 = ((IWriter writer, int value) => writer.WriteInt(value)); 
Action<IWriter, int[]> lambda2 = ((IWriter writer, int[] value) => 
    { 
     lambda4(writer, ((IEnumerable<int>) value).Count()); 
     WriteCollectionElements((IEnumerable<int>)value, writer, lambda3); 
    }); 
Action<IWriter, TheData> lambda1 = ((writer, data) => 
    { 
     lambda2(writer, data.a); 
     lambda3(writer, data.b); 
    }); 
class TheData { int[] a; int b; } 

Lambda1和Lambda2隱含捕捉變量的操作：在lambda2表達：
「lambda2含蓄抓獲關閉」在lambda1表達

對此的解釋是here和here：
「lambda4隱式捕捉閉合」。如果刪除WriteCollectionElements行，則警告消失。實質上，JIT編譯爲內部表達式調用創建一個包裝類，捕獲作者和匿名類型的VALUES，以便將BeginWritingCollection的操作傳遞給WriteCollectionElements靜態方法。

的解決辦法是從lambda2報表內嵌到lambda1

Action<IWriter, int> lambda4 = ((IWriter writer, int length) => writer.BeginWritingCollection(length)); 
Action<IWriter, int> lambda3 = ((IWriter writer, int value) => writer.WriteInt(value)); 
Action<IWriter, TheData> lambda1 = ((writer, data) => 
    { 
     lambda4(writer, ((IEnumerable<int>) value.a).Count()); 
     WriteCollectionElements((IEnumerable<int>)value.a, writer, lambda3); 
     lambda3(writer, data.b); 
    }); 
class TheData { int[] a; int b; }