Operator Traits

Operator Overloading

• This is an "easy, boring" chapter

• There are traits that can be used to tell the Rust compiler to use standard operators for your standard type

• Compromise between Nickle-style ("operator overloading makes programs unreadable") and C++-style ("overload any operator for any reason anytime")

What You Cannot (Must Not) Do

• Cannot change precedence or associativity of standard operators

• Overloaded operators are "expected" (not required, but really?) to obey basic arithmetic laws "as appropriate", for example

  • Associativity of *

    a * (b * c) == (a * b) * c

  • Transitivity of inequality

    a < b < c ⇒ a < c

• In general, it is good style to not be polymorphic with operators, e.g. 1.0 + 2 should maybe be rejected

What You Can Do

• Pick any operator from the table in the chapter and specify its function on your own datatypes (examples/matmul.rs)

• The arithmetic operators consume their arguments. Sorry. Usually derive Copy for arithmetics

• Compound assignment operators are separate. They should be derivable, but currently aren't

• Index and IndexMut allow overloading [] in various contexts. IndexMut requires producing a reference to valid memory, which is borked for types that want to do an initial assignment