Consider obtaining method infos from compiler generated expressions (may help with UWP/.NET Native)

[divega]

Queryable uses this pattern:

       public static IQueryable<TSource> Where<TSource>(
           this IQueryable<TSource> source, 
           Expression<Func<TSource, bool>> predicate) 
       { 
           if (source == null) 
               throw Error.ArgumentNull("source"); 
           if (predicate == null) 
               throw Error.ArgumentNull("predicate"); 
           return source.Provider.CreateQuery<TSource>( 
               Expression.Call( 
                   null, 
                   GetMethodInfoOf(() => Queryable.Where( 
                       default(IQueryable<TSource>), 
                       default(Expression<Func<TSource, bool>>))), 
                   new Expression[] { source.Expression, Expression.Quote(predicate) } 
                   )); 
       } 
...
       private static MethodInfo GetMethodInfoOf<T>(Expression<Func<T>> expression) 
       { 
           var body = (MethodCallExpression)expression.Body; 
           return body.Method; 
       } 

We haven't tested yet if this actually helps but it avoids using reflection directly at runtime and in particular MakeGeneticMethod<T>() which is known to be problematic with .NET Native.

cc @natemcmaster @anpete

[rowanmiller]

@natemcmaster you may want to do this earlier to reduce directives for .NET Native

[natemcmaster]

This won't work. LINQ uses Type.MakeGenericMethod under the hood.
See
https://github.com/Microsoft/referencesource/blob/74706335e3b8c806f44fa0683dc1e18d3ed747c2/System.Core/Microsoft/Scripting/Ast/MethodCallExpression.cs#L999.

[divega]

Interesting. Then does Queryable currently not work at all in .NET Native?

[natemcmaster]

The problem is in Expression.Call. The overload used in the example above does not trigger a call to MakeGenericMethod

[divega]

Still don't understand why it wouldn't work for us, sorry about that 😄 Will probably ask you in person.

[natemcmaster]

Discussed in person. Will investigate more.

[natemcmaster]

After further investigation, refactoring our code to avoid calls to MakeGenericMethod is unnecessary, at least for the sake of .NET Native. With RuntimeTypeDiscoverer and the Scaffold-Directives command (see #4197), we can generate most of the rdxml necessary to make these calls work in current UWP tooling. Furthermore, updates to .NET Native include bug fixes that alleviate these problematic scenarios. I recommend closing this issue.

[divega]

Closing as per @natemcmaster's comment.