Protocol: Guarantee

[oscbyspro]

Trusted inputs have multiple conveniences that can be derived from a simple protocol:

protocol Guarantee<Value> {

    associatedtype Value
    
    static func predicate(_ value: borrowing Value) -> Bool
    
    init(unchecked value: consuming Value)
}

[oscbyspro]

The only problem is that it duplicates validation checks in debug mode, but I also don't want init(unsafe:).

[oscbyspro]

Hm. I could require that it only stores its value, adding some abstract capabilities. Alternatively, I can omit that and mark Divider<T> (#58) as a Guarantee. I mean, it's basically a trusted input with some additional data.

[oscbyspro]

Meh. It's not enough boilerplate to worry about.

[oscbyspro]

I might want to add this kind of protocol simply to aid prototyping of various trusted input types (#78). It also simplifies testing since derived operations are identical for all types. Something like the following, perhaps?

public protocol Guarantee<Value> {
    
    associatedtype Value
    
    @inlinable static func predicate(_ value: borrowing Value) -> Bool
    
    @inlinable init(unsafe value: consuming Value)
        
    @inlinable consuming func payload() ->  Value
}