Function associativity 

fn associativity(op: AssocOp) -> Associativity

Returns the associativity/fixity of an operator. The difference with AssocOp::fixity is that an operator can be both left and right associative (such as +: a + b + c == (a + b) + c == a + (b + c).

Chained as and explicit : type coercion never need inner parenthesis so they are considered associative.