String interpolation and formatting

Interpolation basics

Prefix a string literal with $ to make it interpolated: any {expression} inside is evaluated and its ToString() spliced into the result. The expression can be a variable, a property, a method call, or arithmetic — $"{a} + {b} = {a + b}". To print a literal brace, double it: {{ becomes { and }} becomes }.

Interpolation is the modern replacement for String.Format("{0} {1}", a, b), where you had to match numbered placeholders to arguments by position. The interpolated form reads in source order, so there is nothing to mis-count.

Format and alignment specifiers

Inside a placeholder you can append two optional clauses after the expression: {value,alignment:format}.

• The format clause (after :) is a standard or custom format string. Common standard ones: N2 (number, 2 decimals, group separators), C (currency), P (percent, scales by 100), F3 (fixed-point, 3 decimals), X (uppercase hex), D5 (integer padded to 5 digits). Custom patterns like 0.0 or yyyy-MM-dd work too.
• The alignment clause (after ,) is a minimum field width: positive right-aligns, negative left-aligns, padding with spaces. {name,-10} left-aligns in a 10-wide column.

Both are optional and order matters — alignment comes first, then the colon-format: {total,12:N2}.

Raw string literals

A raw string literal is delimited by three or more double-quotes ("""). Inside, backslashes and quotes are literal — no escaping — which makes JSON, regex, and file paths far cleaner. When the opening """ is on its own line, the closing """ sets the indentation: whitespace to the left of the closing delimiter is stripped from every line, so you can indent the literal to match your code.

Raw literals also interpolate: prefix with $ and use a single { }. If your content itself contains braces, add more dollar signs — $$"""...""" makes {{ the interpolation delimiter so single braces stay literal.