Operator overloading in Go with contracts
Roger Peppe 2018-09-03
[Edit 2018-09-11 Reworked following feedback from @jba]
In his Go generics feedback document, Dominic Honnef writes "Contracts are nice, but where is the operator overloading?". In this document, I set down some thoughts about how operator overloading might be added to Go within the context of the new generics design, layered on top of the current design.
The central part would be a new package in the standard library. This package would hook a type-parameterized type up to chosen Go operators. The Go compiler would know how to rewrite operator syntax into method call syntax on associated interface methods. How that's done is implementation-defined, and the API itself is defined by a package, but contracts supply a way of reasoning about available operators without defining the mapping between operators and method names.
The compiler would be responsible for making sure exist