[swift-evolution] ternary operator ?: suggestion

[Paul Ossenbruggen]

Like the switch statement, I think it would help to at least optionally be able to have parenthesis around the cases. It gives it a more structure that I think the “case” and “default” need and it would encourage indenting which I think helps a lot. But I think it might not be a bad thing to require the parenthesis. for the switch like flavor. I think parenthesis are better because it is an expression and it should feel more like a function, but that is open for debate. 

let commission = trade ?{
case .Buy(let quantity, let price) where Double(quantity) * price > 10000:
    Double(quantity) * price * vipCommissionRate / 100
case .Buy(let quantity, let price):
    Double(quantity) * price * commissionRate / 100
case .Sell(let quantity, let price) where Double(quantity) * price > 10000:
    Double(quantity) * price * vipCommissionRate / 100
case .Sell(let quantity, let price):
    Double(quantity) * price * commissionRate / 100
)

But if we go with brackets then I would recommend something like this: 

let commission = match (trade) {
case .Buy(let quantity, let price) where Double(quantity) * price > 10000:
    Double(quantity) * price * vipCommissionRate / 100
case .Buy(let quantity, let price):
    Double(quantity) * price * commissionRate / 100
case .Sell(let quantity, let price) where Double(quantity) * price > 10000:
    Double(quantity) * price * vipCommissionRate / 100
case .Sell(let quantity, let price):
    Double(quantity) * price * commissionRate / 100
}

Which is much more statement like and may make the expression vs statement distinction harder to see and explain. And we lose terseness for the simple single line case. Anyway, I think the cases need to be indented and have some indication when they are complete to add balance. 


> On Jan 7, 2016, at 2:14 AM, Craig Cruden <ccruden at novafore.com> wrote:
> 
> If the `where` clause is omitted it would make the following sample code a little more complex than it would need to be:
> 
> public enum Trade {
>     case Buy(quantity: Int, price: Double)
>     case Sell(quantity: Int, price: Double)
> }
> 
> let vipCommissionRate = 1.25
> let commissionRate = 2.50
> 
> let trade = Trade.Buy(quantity: 400, price: 12.50)
> 
> let commission: Double
> 
> let commission = trade ?
> case .Buy(let quantity, let price) where Double(quantity) * price > 10000:
>     Double(quantity) * price * vipCommissionRate / 100
> case .Buy(let quantity, let price):
>     Double(quantity) * price * commissionRate / 100
> case .Sell(let quantity, let price) where Double(quantity) * price > 10000:
>     Double(quantity) * price * vipCommissionRate / 100
> case .Sell(let quantity, let price):
>     Double(quantity) * price * commissionRate / 100
> 
> 
> 
>> On 2016-01-07, at 15:19:48, Craig Cruden <ccruden at novafore.com <mailto:ccruden at novafore.com>> wrote:
>> 
>> On the where/if conditional clause being omitted…. if that is done it will lead to more convoluted code since people will end up nesting in ternary below the “switch/match” to accomplish that where a simple filter would have left it at one level of code.
>> 
>> 
> 

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