Tuples vs. Structs

Tuples and structs both group several values into one. The difference is how the parts are identified: a tuple's elements are positional and anonymous, while a struct's fields are named.

When a Tuple Fits

Reach for a tuple when the grouping is small, local, and self-evident — typically returning two or three closely related values:

func Divide(a: int, b: int) -> (int, int) {
    return (a / b, a % b);   // quotient and remainder
}

let (q, r) = Divide(17, 5);

Here the meaning of each position is obvious at the call site, and a named type would add ceremony without adding clarity.

When to Prefer a Struct

Nothing at the call site says what each tuple position means. When a tuple would accumulate more than two or three elements, or when the meaning of a position is not obvious, prefer a struct with named fields:

// Hard to read at the call site — what do the three values mean?
func Parse(src: Slice<char8>) -> (int, int, bool) { /* … */ }

// Self-documenting
struct ParseResult {
    line: int;
    column: int;
    ok: bool;
}

func Parse(src: Slice<char8>) -> ParseResult { /* … */ }

A struct also lets the type be named, reused, given methods, and extended with new fields without rewriting every call site.

Rule of Thumb

See Also

• Tuples — the tuple overview
• Structures — named aggregates with typed fields
• Methods — attaching behaviour to a struct