Is an Inner Function Justified in this Situation

Question

I'm new to the functional programming concepts in C#, but I have some experience with higher order functions via Haskell, Scala, Python and Ruby. I'm currently going through an old .NET 2.0 codebase with a LOT of duplication in it. Most of it is simple "copy/paste" with a few variables changed. I'm trying to condense as much of this as possible.

A chunk of code within a routine I'm working on now goes a bit like this, for example:

if (PostProcess.UsesFirstPass)
{
    w.WriteLine(V1 + " = 0" + " !! SET FOO");
    w.WriteLine(V2 + " = 0" + " !! SET BAR");
    w.WriteLine(V3 + " = 0" + " !! SET BAZ");
    if (PostProcess.IsSpecial){
        w.WriteLine(V3 + " = 20" + " !! INCREASE BAZ");
    }
    w.WriteLine(V4 + " = 0" + " !! SET QUUX");
}
if (PostProcess.UsesSecondPass)
{
    w.WriteLine(V5 + " = 0" + " !! SET FOO");
    w.WriteLine(V6 + " = 0" + " !! SET BAR");
    w.WriteLine(V7 + " = 0" + " !! SET BAZ");
    if (PostProcess.IsSpecial){
        w.WriteLine(V7 + " = 20" + " !! INCREASE BAZ");
    }
    w.WriteLine(V8 + " = 0" + " !! SET QUUX");
}
if (PostProcess.UsesFinalPass)
{
    w.WriteLine(V9 + " = 0" + " !! SET FOO");
    w.WriteLine(V10 + " = 0" + " !! SET BAR");
    w.WriteLine(V11 + " = 0" + " !! SET BAZ");
    if (PostProcess.IsSpecial){
        w.WriteLine(V11 + " = 20" + " !! INCREASE BAZ");
    }
    w.WriteLine(V12 + " = 0" + " !! SET QUUX");
}

Where any of the "V"s you see in there is a string variable defined earlier. It's part of a fairly large method. I could write another method called, say, WriteVariables() and pass in the required info and call it three times, but it only ever applies to this section of method. I think this would be a place where writing an anonymous inner function would make sense.

I did it to test it out, and it seems to work fine. Now I have a single delegate that looks something like:

private delegate void WriteCutVars(string V1, 
    string V2, string V3, string V4, CuttingParameters cutParam);

// snip //

WriteCutVars WriteVars = (Va, Vb, Vc, Vd) => {
    w.WriteLine(Va + " = 0" + " !! SET FOO");
    w.WriteLine(Vb + " = 0" + " !! SET BAR");
    w.WriteLine(Vc + " = 0" + " !! SET BAZ");
    if (PostProcess.IsSpecial){
        w.WriteLine(Vc + " = 20" + " !! INCREASE BAZ");
    }
    w.WriteLine(Vd + " = 0" + " !! SET QUUX");
}
if (Process.UsesFirstPass) WriteVars(V1, V2, V3, V4);
if (Process.UsesSecondPass) WriteVars(V5, V6, V7, V8);
if (Process.UsesFinalPass) WriteVars(V9, V10, V11, V12);

My main questions:

• Is this a proper use of inner functions?
• Is this acceptable when I'm the only CS graduate on a team of mostly mechanical engineers?

Answer 1

Your implementation seems reasonable to me.

However, if most of the other people developing the software have limited advanced programming experience you might want to use a regular function instead of an anonymous one since it will be more obvious what's going on.

When you're the senior developer and the rest of your team is at a significantly lower skill level; making sure they understand how your code works and can easily modify it if needed is an important consideration. Since your team mostly consists of non-programmers this is a larger consideration, since for programming techniques they probably congregate closer to the Use What I Know end of the scale than the Learn New Things Everyday end.

Breaking the repeated logic out and removing the copy/pasting should be simple to explain the benefits of. More advanced techniques like anonymous functions or linq would be a harder sell since they don't give major and obvious functional/maintenance improvements. The hardware engineers I've worked with in the past mostly only learned C in college since it was the language of choice for the micro-controllers in the gadgets they were building. With only a handful of classes their skills were concentrated on practical basic programming only, and not anything advanced.

Answer 2

This is not a higher-order function, so it should be easily understandable to any C# programmer.

Although instead of using a custom delegate type, you could've used Action<string, string, string, CuttingParameters>.

But I think a normal method would have been fine here too, and is probably more idiomatic. Even if you won't use it anywhere else.

Answer 3

The key question is whether to use a "normal" private function or a strictly local function and the answer should stem from the same decision-making you'd use with a private field vs. a local variable: Is this thing useful anywhere but this function? In this case, it would appear not, so your approach seems correct.

There is an issue with using advanced functional techniques in C#, but C# is evolving to have more and more functional features, so you ought not avoid all functional techniques only because they may still be unfamiliar. I would say that this would actually be the type of use that would be good in a codebase where people were relatively unfamiliar with functional programming, since it is very straightforward in both utility and implementation.