§9 String Interpolation

let name = "Sailfin";
let greeting = "Hello, {{ name }}!";         // "Hello, Sailfin!"
let math = "2 + 2 = {{ 2 + 2 }}";           // "2 + 2 = 4"
let nested = "User: {{ user.name.trim() }}"; // arbitrary expressions

Mandatory double braces. Whitespace at the edges is ignored: {{name}} and {{ name }} are equivalent. The compiler lowers interpolated strings into segment arrays evaluated at runtime.

Primitive optional unions such as int | null render the active non-null payload in direct, flow-narrowed, and match-bound positions.