How to invoke a C# method inside a Q# operation?

Question

Suppose there is a Q# operation as follows:

operation Op () : Bool {

    let result = CSharpMethod ();
    return result
}

where CSharpMethod () is a defined method in the Driver class as follows:

public static bool CSharpMethod () {
    // ...
    // return a boolean value
}

So my question is how to call a method of a C# class inside a Q# operation and handle its returned value?

Thanks.

Answer 1

Q# operations are compiled into C# classes. To define a C# implementation for a Q# operation, you will need to do the following steps:

1. Define a Q# operation with empty or intrinsic body CSharpMethod.
2. Define a C# class that implements the abstract class into which your Q# operation gets compiled, something like public class CSharpMethod_Impl : CSharpMethod.
3. Define method called Body in that class that does the actual computation that you need and returns the result.

This is a very hacky thing to do, so you might want to follow an example of operation GetOracleCallsCount and its C# implementation to see the exact pieces that have to be in place for it to work.

You can also see this question on StackOverflow that tries to do a similar thing.