C#: log variable name and value using function expression

Question

In code which regularly needs debug logging, I end up with large blocks of code such as:

int someVar = 1;
bool anotherVar = true;
//...
string lastVar = "foo";

// littered through the code
Log._Debug(
   "arbitrary message string", 
   $"{nameof(someVar)} = {someVar} " +
   $"{nameof(anotherVar)} = {anotherVar} " +
   // ...
   $"{nameof(lastVar)} = {lastVar} "
);

These debug blocks can sometimes be huge (20+ vars being logged) and they can occur dozens of times in a class making the whole thing completely unreadable. Sadly they're necessary - sometimes we need to send debug builds to users (they can't run debugger, it's easier just to get them to run the debug build and send us the logs). It's also old code base which is why it's such a freaking mess.

I'm trying to find a way to debloat the debug chunks in the code, just to make it less depressing to maintain lol.

In my quest to find cleaner syntax, I found https://stackoverflow.com/a/9801735 which shows how to get member name from a lambda function. Which made me wonder, is it possible to create something a bit like this...?

Log._Dump(
   "arbitrary message string", 
   () => somevar,
   () => anotherVar,
   // ...
   () => lastVar
);

So I tried creating a method using params as follows:

[Conditional("DEBUG")]
public static void _Dump(string message, params Func[] vars) {
                                             // ^ what <T> do I use?
}

private static string GetMemberName<T>(Expression<Func<T>> memberExpression) {
    // this would eventually return $"{memberName} = {memberValue}"
    // which, btw, I have no idea if that's even possible yet
    // but I didn't get that far as still trying to work out how to do
    // the _Dump() method params above :/

    MemberExpression expressionBody = (MemberExpression)memberExpression.Body;
    return expressionBody.Member.Name;
}

I don't know how to do params array of functions with varying return types.

I could potentially just make the params a string array and do the GetMemberName manually for each lambda, for example:

private string NV<T>(Expression<Func<T>> memberExpression) {
  // ...code...

  return $"{memberName} = {memberValue}";
}

Log._Dump(
   "arbitrary message string", 
   NV(() => somevar),
   NV(() => anotherVar),
   // ...
   NV(() => lastVar)
);

But that's adding boilerplate to the code again which is what I'm trying to avoid. Is there any way I can get it working without that extra NV() wrapper?

EDIT: It's really old codebase and we're stuck with .Net Framework 3.5 so limited to C# 6 or something like that.

logging variable names is not a common practice, this should be the debugging process. — Lei Yang, Mar 22 '22 at 01:03

score 1 · Accepted Answer · answered Mar 22 '22 at 01:54

C# 10 introduced [CallerArgumentExpression] (docs), a way to pass a string representation of the callers source code. So you could write a helper method;

public void Log<T>(T value, [CallerArgumentExpression("value")] string name=null)
  => Log($"{name} = {value}");

But you could also combine this with another new feature, [InterpolatedStringHandler] (docs) to log the name of any variable inside an interpolated string.

[InterpolatedStringHandler]
public ref struct DebugLogHandler
{
    private readonly StringBuilder sb;
    public DebugLogHandler(int literalLen, int formattedCount)
    {
        sb = new StringBuilder(literalLen);
    }
    public void AppendLiteral(string s) => sb.Append(s);
    public void AppendFormatted<T>(T value, [CallerArgumentExpression("value")] string name=null)
    {
        sb.Append(name);
        sb.Append("=");
        sb.Append(value?.ToString());
    }
    public string BuildMessage() => sb.ToString();
}

public static void Log(string message) { ...TODO... }
public static void Log(DebugLogHandler builder)
    => Log(builder.BuildMessage());

var variableName = "value";
Log($"Something {variableName}");

Ah, we're stuck on old version of .Net Framework 3.5 so if memory serves we're limited to C# 6 or something like that :( — cabbageforall, Mar 22 '22 at 02:18

C#: log variable name and value using function expression

1 Answers1