5.3 Overloading and user-defined operators

Overloading built-in operators — op declarations in impl:

impl Vec3 {
  static op +(a: Vec3, b: Vec3) -> Vec3 => Vec3(a.x + b.x, a.y + b.y, a.z + b.z)
  static op *(v: Vec3, k: f32) -> Vec3 => Vec3(v.x * k, v.y * k, v.z * k)
  static op -(v: Vec3) -> Vec3 => v * -1.0
  op [](i: usize) -> f32 { … }            // read by index
  var op [](i: usize) -> &var f32 { … }   // write by index
  op ()(t: f32) -> Vec3 { … }             // call as a function
  static op <=>(a: Vec3, b: Vec3) -> Ordering { … }
  op as Vec4 => Vec4(x, y, z, 1.0)
}

• Overloadable: arithmetic, bitwise, comparisons via <=>, [], (), as, compound assignments.
• NOT overloadable: && || ?? ?. ? ! is = -> ?-> ~> !> |> =>, ., ...
• a op= b by default means a = a op b; a declaration var op += replaces this behaviour.
• ==/!= come from Eq; <, <=, >, >= come from <=> (Ord).
• There are no implicit conversions; op as T is called only by an explicit x as T.

User-defined operators:

operator <|> <T>(a: Parser<T>, b: Parser<T>) -> Parser<T>  infixl 3 => a.orElse(b)
operator ~~ (s: str, re: Regex) -> bool                      infix 4 => re.matches(s)
operator ^^ (a: f64, b: f64) -> f64                          infixr 12 => a.pow(b)
operator ¬ (b: Bits) -> Bits                                prefix => b.invert()

• The operator symbol is a sequence of + - * / % < > = ! & | ^ ~ ? . or Unicode characters of categories Sm/So. The sequence MUST NOT coincide with a built-in operator or delimiter and MUST NOT start with // or /*.
• Fixity: infixl N, infixr N, infix N (N is a level 1–12 from table 5.2) or prefix (level 14). There are no postfix user-defined operators.
• An operator is an ordinary declaration with visibility; in another module it is used only after an explicit import (use parsers { <|> }).
• Any function of two arguments can be called infix: a `max` b (level 4, non-associative).

Related diagnostics

not-callable, not-overloadable, operator-decl, range-not-iterable

Source: docs/spec/oxl-standard.en.md