Compiling recursive methods

[sebastienros]

In the default implementation it's not possible to "compile" recursive methods. I think it fails at runtime last time I tried.
Do you think FEC would support that?

[dadhi]

I am not sure, but don't think anything prevents it. Did you try it with FEC?
Or do you mean the tail-recursive methods?

[sebastienros]

Fair, but based on the answer I wonder if the user code expression tree creation should be responsible for handling the closure class creation and usage. Maybe the standard compiler detects the closure and creates the plumbing, while FEC doesn't.

[jogibear9988]

Think it would be okay. It only should throw that you know why it wont work.
Don't know if recursion should be in scope of Expression Trees

[dadhi]

@jogibear9988 @sebastienros
I found the cause of the issue. FEC closure variables are immutable and cannot be set outside of the nested lambda after lambda is compiled (emitted and stored into the parent closure). You may hack it by using the array of one element as a variable.. check the code from
here

FastExpressionCompiler/test/FastExpressionCompiler.IssueTests/Issue293_Recursive_Methods.cs

Line 51 in 95d1d39

// This should work:

Now I need to find a simple way to detect this situation and return null from the Compiler instead of throwing.

[sebastienros]

I also fixed it by creating a closure class that holds the Func in a field, and pass an instance of this class, like what the compiler is doing as explained in the SO answer by Eric Lippert. I can even reuse the same instance from multiple compiled lambdas.

[dadhi]

Good, I have opened an issue #295 to make it possible in FEC. I just need to create the closure items array and change the variable assignement to array element assignment and usage (for the variables passed to closure).