try this

erase.swift

struct ExpressionErased : Chainable {
    var chainType: SQLiteChainType = .None
    let __andOperator:((rhs:Chainable) -> [Chainable])
    
    init<T : Chainable>(expression:T) {
        self.__andOperator = expression.andOperator
    }
    
    func andOperator(rhs: Chainable) -> [Chainable] {
        return self.__andOperator(rhs: rhs)
    }

}


//Usage

let oneWithIntErased = ExpressionErased(expression: oneWithInt)
let oneWithDoubleErased = ExpressionErased(expression: oneWithDouble)

let myBagOfGoodies =  [oneWithIntErased, oneWithDoubleErased]