I have two strings (aggregatePath and pathFromParent), either of which might be null or an empty string. I want to concatenate the two strings with a separator only if neither is null or empty. This is what I've ended up with:

FullPath =
    aggregatePath +
    aggregatePath is not (null or "") && pathFromParent is not (null or "") ? "." : "" +

but it seems overly complex for what I'm trying to do.

How can I better clarify the intent of this code?

I'm not asking about performance. I've just come back to this code after a while, and it took me a few moments to figure out the intent. Is there perhaps some better idiom for this?

Using C# 9.

  • 1
    \$\begingroup\$ string.Join(".", paths.Where(x => x != null)) where paths = new List<string>{aggregatePath , pathFromParent}. \$\endgroup\$
    – BCdotWEB
    Commented Jul 6, 2021 at 8:03
  • \$\begingroup\$ @BCdotWEB I was thinking to use an array, but it still doesn't feel clear -- why am I creating this new instance of array/List<string>? (NB. I'm checking for both null and "".) \$\endgroup\$
    – Zev Spitz
    Commented Jul 6, 2021 at 8:05
  • \$\begingroup\$ If you want more clarity why not simply write things down explicitly, e.g if (string.IsNullOrEmpty(first) || string.IsNullOrEmpty(second)) { seperator = string.Empty }. You can use string.Join (separator, first, second) afterwards. \$\endgroup\$
    – devsmn
    Commented Jul 6, 2021 at 8:11
  • \$\begingroup\$ FullPath = $"{aggregatePath}{(aggregatePath?.Length > 0 && pathFromParent?.Length > 0 ? "." : "")}{pathFromParent}"; \$\endgroup\$
    – aepot
    Commented Jul 6, 2021 at 13:40

2 Answers 2


In my opinion, the best way to clarify your intention is to write down things explicitly.

Start by setting the separator to . by default.

string separator = ".";

Then, use string.IsNullOrEmpty to check whether one of the two strings is either null or string.Empty and set the separator to string.Empty if that's the case.

if (string.IsNullOrEmpty(aggregatePath) || string.IsNullOrEmpty(pathFromParent)) {
    separator = string.Empty;

Lastly, join the two string using string.Join.

string.Join (separator, aggregatePath, pathFromParent);

Might not be that fancy but it's quite easy to understand.

Try it out yourself.

  • \$\begingroup\$ My subjective feeling about this is that pulling out the separator into a separate variable is both clear and concise. But I'll accept your answer because it does answer the question. \$\endgroup\$
    – Zev Spitz
    Commented Jul 6, 2021 at 8:28

The following avoids temporary variables and unnecessary concatenation.

return string.IsNullOrEmpty(aggregatePath)
    ? pathFromParent
    : string.IsNullOrEmpty(pathFromParent)
        ? aggregatePath
        : aggregatePath + "." + pathFromParent;

If you don't find ternary expressions clear, you could expand it to if-statements, but I don't think that's necessary.


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