intersection types¶

basedpython adds an & operator for intersection types in annotation positions, mirroring the existing | for unions:

def render(x: Drawable & Serializable) -> bytes: ...

handlers: list[HasName & HasId]

cb: (A & B) | C

transpiles to:

def render(x: Intersection[Drawable, Serializable]) -> bytes: ...

handlers: list[Intersection[HasName, HasId]]

cb: Intersection[A, B] | C

semantics¶

A & B is the type of values that satisfy both A and B. left-associative chains are flattened: A & B & C becomes Intersection[A, B, C] rather than nested. intersections compose with unions by precedence: & binds tighter than |, so A & B | C parses as (A & B) | C

scope¶

the & operator is recognized only in syntactic type positions: annotations, return types, type aliases, and subscript slices that are themselves type contexts. bitwise AND in value expressions is untouched:

x = A & B   # bitwise AND — unchanged
a: A & B    # intersection — rewritten

polyfill¶

Intersection is imported from ty_extensions (basedpython's type-extension module). there is no native runtime equivalent — intersections are a type-checker-only construct, evaluated by ty