Databases
StackOverflow2013
Postsdbo
POCompiling a lambda expression results in delegate with Closure argument
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POCompiling a lambda expression results in delegate with Closure argument
    primarykey
    data
    text
    <p>When I use <code>Expression.Lambda( ... ).Compile()</code> in order to create a delegate from an expression tree, the result is a delegate of which the first argument is <a href="http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.closure.aspx"><code>Closure</code></a>.</p> <pre><code>public static Func&lt;T, T, T&gt; CreateTest&lt;T&gt;() { ParameterExpression a = Expression.Parameter( typeof( T ) ); ParameterExpression b = Expression.Parameter( typeof( T ) ); Expression addition = Expression.Add( a, b ); return (Func&lt;T, T, T&gt;)Expression.Lambda( addition, a, b ).Compile(); } ... // 'addition' equals // Int32 lambda_method( // System.Runtime.CompilerServices.Closure, // Int32, // Int32 ) Func&lt;int, int, int&gt; addition = DelegateHelper.CreateTest&lt;int&gt;(); int result = addition( 5, 5 ); </code></pre> <p>I can easily call the delegate through ordinary code without passing a <code>Closure</code> object, but where does this <code>Closure</code> come from?</p> <p>How can I call this delegate dynamically?</p> <pre><code>// The following does not work. // Exception: MethodInfo must be a runtime MethodInfo object. MethodInfo additionMethod = addition.Method; int result = (int)additionMethod.Invoke( null, new object[] { 5, 5 } ); </code></pre> <p>Using expression trees it looks like I have to pass the <code>Closure</code> object.</p> <pre><code>PropertyInfo methodProperty = typeof( Delegate ).GetProperty( "Method", typeof( MethodInfo ) ); MemberExpression getDelegateMethod = Expression.Property( Expression.Constant( addition ), methodProperty ); Func&lt;MethodInfo&gt; getMethodInfo = (Func&lt;MethodInfo&gt;)Expression.Lambda( getDelegateMethod ).Compile(); // Incorrect number of arguments supplied for call to method // 'Int32 lambda_method(System.Runtime.CompilerServices.Closure, Int32, Int32)' Expression call = Expression.Call( getMethodInfo(), Expression.Constant( 5 ), Expression.Constant( 5 ) ); </code></pre> <p>This is a simplified example which doesn't make sense in its own right. What I am actually trying to achieve is to be able to wrap e.g. <code>Func&lt;Action&lt;SomeObject&gt;&gt;</code> with <code>Func&lt;Action&lt;object&gt;&gt;</code>. I can already do this for non nested delegates. This is useful during reflection, <a href="http://whathecode.wordpress.com/2011/07/02/casting-to-less-generic-types/">as discussed here</a>.</p> <p>How should I correctly initialize this <code>Closure</code> object, or how do I prevent it from being there?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USSteven Jeuris
    1. USSteven Jeuris
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POCompiling a lambda expression results in delegate with Closure argument
      1. USBLUEPIXY
      1. VTFavorite
    2. VO
      singulars
      1. POCompiling a lambda expression results in delegate with Closure argument
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POCompiling a lambda expression results in delegate with Closure argument
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO@JonSkeet: I'll do my best, the problem is the total example is quite complex. I am attempting to call a previously compiled delegate recursively. While I try to extract a small subset of the problem, [here](http://pastebin.com/53f0VqnF) you can already find the entire function.
      singulars
      1. POCompiling a lambda expression results in delegate with Closure argument
      1. USSteven Jeuris
    2. COYeah, making it shorter would certainly help :)
      singulars
      1. POCompiling a lambda expression results in delegate with Closure argument
      1. USJon Skeet
    3. CO@JonSkeet: As a bit more information, the goal would be to allow creating wrapper functions so e.g. `Action<Action<SomeType>>` could be wrapped by `Action<Action<object>>`. This continues on [my previous implementation](https://github.com/Whathecode/Framework-Class-Library-Extension/blob/master/Whathecode.System/DelegateHelper.cs) which can only do this for `Action<SomeType>` to `Action<object>`.
      singulars
      1. POCompiling a lambda expression results in delegate with Closure argument
      1. USSteven Jeuris
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload