The concept of using operators to implement methods cross-pollinated in my mind
with Patrick’s “Go Generics with Adaptors” thought experiment and produced
this: https://gist.github.com/andybalholm/acecba3acf57bf1254142dadce928890
<https://gist.github.com/andybalholm/acecba3acf57bf1254142dadce928890>
Here is the core of the proposal (the gist of the gist?):
Contracts
In this proposal, a contract is a list of type-specific functions that are
needed to implement a generic algorithm. Generally, it will contain default
implementations for these functions, but these are optional. (If default
implementations are not included, an adapter will always be necessary.) The
default implementations are unconstrained generic code; if they compile
successfully with a given set of type parameters, those parameters fulfill the
contract.
contract Adder(T) {
Zero() T {
return 0
}
Add(a, b T) T {
return a + b
}
}
A generic function that uses a contract calls the functions in the contract to
perform operations on generic values:
func SumSlice(type T Adder)(s []T) T {
sum := Zero()
for _, t := range s {
sum = Add(sum, t)
}
return sum
}
<https://gist.github.com/andybalholm/acecba3acf57bf1254142dadce928890#adaptors>Adaptors
A type that doesn't work with a contract's default implementation can still
fulfill the contract by means of an adaptor. An adaptor is a type that fulfills
the interface defined by a contract. When an adaptor is being used, calls to
the contract’s functions are implemented by calls to the corresponding methods
of the adaptor’s zero value.
type BigIntAdder struct {}
func (BigIntAdder) Zero() *big.Int { return new(big.Int) }
func (BigIntAdder) Add(a, b *big.Int) *big.Int { return new(big.Int).Add(a, b) }
The adaptor is specified along with the type parameters when instantiating a
generic function or type:
var bigints []*big.Int
fmt.Println(SumSlice(*big.Int, BigIntAdder)(bigints))
Andy
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