Combine string interpolation and string.format

Question

I'm just wondering if there is a possibility to combine string interpolation, which was introduced in C# 6.0 and string.format? Any smarter ideas like this?

string fancyString = $"My FancyString was created at { DateTime.Now }" + " and I want to add some static with string.format like {0}";

Answer 1

Escape your {0} by writing it as {{0}} so string interpolation leaves it alone. Then you can pass the string into string.Format to replace the {0}.

For those wondering why you'd want to do this, I can imagine one possibility where you want to do some sort of reusable template such as:

var urlTemplate = $"<a href='{BaseHref}/some/path/{{0}}'>{{1}}</a>";

var homeLink = string.Format(urlTemplate, "home.html", "Home");

var aboutLink = string.Format(urlTemplate, "about.html", "About Us");

Of course this example is too simple to warrant such a technique, but imagine if you had a template with a very large number of variables and you only cared to change a couple from one rendered template to the next. This would be much more readable than having {32}, {33}, {34}... etc. in your template.