Write other C# code in an interpolated string?

Question

In C# 11 we can now include newlines in an interpolated string. So we can write code like this:

    string pageTitle = "";
    string header = $"Header: {
      pageTitle switch
      {
        "" => "No title",
        _ => pageTitle
      }}";

Is there a way to write other code here beyond the switch statement?

I tried an if and it tells me that if is an invalid expression term.

    string header51 = $"Header: {
      if (pageTitle5 == "")
      {
        "No title";
      }
      else
      {
        pageTitle5;
      }  
    }";

Are there other statements beyond switch that work here?

it needs expression not statment. do pageTitle==""?"No title":PageTitle — pm100
– pm100, Commented Apr 6, 2023 at 20:48
Side note: code in the question does not have "the switch statement"...(medium.com/@time4ish/…) — Alexei Levenkov
– Alexei Levenkov, Commented Apr 6, 2023 at 20:53
The code blocks of interpolated strings must be expressions, they must evaluate to something, or "return" something, which is why the switch expression works because it returns something. Also tangential nitpick: use string.IsNullOrEmpty() which can then be used in a very clean ternary expression -> string header = $"Header: {(string.IsNullOrEmpty(pageTitle5) ? "No Title" : pageTitle5)}" — Narish
– Narish, Commented Apr 6, 2023 at 20:59
Ah! Thank you @AlexeiLevenkov. I was wondering why the syntax didn't match the docs for "switch statement". Thanks for the link. — DeborahK
– DeborahK, Commented Apr 6, 2023 at 21:13

Heinzi · Accepted Answer · 2023-04-06 21:57:40Z

6

Every expression will work. In C#, if is not an expression, but a statement.

However, the ternary operator yields an expression:

string header51 = $"Header: {
  (pageTitle5 == "" 
      ? "No title"
      : pageTitle5)
  }";

switch works in your example, because you do not use the switch statement but a switch expression.

edited Apr 6, 2023 at 21:57

answered Apr 6, 2023 at 20:48

Heinzi

173k61 gold badges386 silver badges555 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Alexei Levenkov Over a year ago

And anything goes if wrapped as IIFE

DeborahK Over a year ago

For anyone else reading this ... the above code doesn't work as is. The ternary operator expression needs to be within parens ( ) to compile.

Fitri Halim · Accepted Answer · 2023-04-07 02:31:13Z

1

If you prefer using if else statement, you can write the code like this :

    string header51 = $"Header:{() =>
    {
        if (pageTitle5 == "")
        {
            return "No title";
        }
        else
        {
            return pageTitle5;
        }  
    }
    }";

This way you have more flexibility to do extra logics in the if else block

answered Apr 7, 2023 at 2:31

Fitri Halim

76910 silver badges19 bronze badges

2 Comments

DeborahK Over a year ago

Nice! So I can pass an anonymous function (or call a named function). Thanks!

Elezar Apr 4 at 1:30

@DeborahK No, this code doesn't work as you would expect. This is just defining the anonymous function, but there's nothing to execute it. It will just call .ToString() on it and use that. So with this code, you would get something like "Header:System.Func`1[System.String]" as the value assigned to header51. You can call a named function though, and since you're actually calling it, its result will be included in the string value. Maybe you could assign an anonymous function to a Func<T> and then execute it, but that seems overly convoluted for most uses.

Collectives™ on Stack Overflow

Write other C# code in an interpolated string?

2 Answers 2

2 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related