String interpolation ^{C# 6.0} allows strings to be built up using a syntax from inside the string itself rather than joining variables together with + which can reduce the noise in many scenarios.

C# 10.0 finally allows you to use this feature for constant strings as well - providing the expressions used within it are all resolvable at compilation time.

Code

Now

const int maxCount = 10;
const int minCount = 5;
const string outOfRangeMessage = $"Value must be between {minCount} and {maxCount}.";

Before

const int maxCount = 10;
const int minCount = 5;
const string outOfRangeMessage = "Value must be between " + minCount +
                                 " and " + maxCount + ".";

More information

• Specification