[swift-users] Pass Value of Variable to a Function

[Michael Sheaver]

Hi Zhao,

Many thanks for your response, and I will give this a try. However, I think that I might have used a bad example for the bigger question I was trying to ask, and for that I am sorry. 

The question that I am really trying to address here is: Is there a more Swift-y way to, when passing a parameter to a function, we can tell it whether:
	a) we intend to pass in the literal string, or
	b) we want to pass the contents of the named variable?

I know that in some languages, if you prepend the passed parameter with a '$', as in $propertyName, the receiving function knows to use the contents of the variable named propertyName (in this case "calendar") instead of the literal string "propertyName". 

Can we easily do this in Swift? If not, why not? Can we propose a change request to implement either a computed property or a method on the Any() class that would allow us to tell a called function whether we are passing in a literal type or a variable that contains the data to be processed?

Maybe this would violate the type safety for which Swift is thankfully so strongly trying to preserve. I don't know, but I would at lest like to consider it, for there ARE good business cases for it.

Does this help to clarify the question. I am posing?

Shawn, let me put this into a Swift file and shoot it your way.

Many thanks!
Michael

> On Sep 6, 2016, at 11:21 PM, Zhao Xin <owenzx at gmail.com> wrote:
> 
> I think you messed up with `Locale` and `NSLocale`.
> 
> `Locale` is a struct in Swift 3 to replace the legacy `NSLocale`. The latter is a class, it has an inner `structure` called `NSLocale.Key`. For `Locale`, there is no `NSLocale.Key`. All there keys are instance properties in `Locale`. So in your specific case, 
> 
> let calendar2 =  (currentLocale as NSLocale).object(forKey:NSLocale.Key(rawValue:propertyName))
> 
> is just almost the same as `let calendar2 = calendar1`.
> 
> If you insist on using `NSLocale.Key`, you should use `NSLocale` instead of `Locale`.
> 
> 
> Zhaoxin
> 
> On Wed, Sep 7, 2016 at 10:35 AM, Michael Sheaver via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
> I am trying to build a table of current locale properties in code, and have encountered issues with trying to pass the value of a variable to a function:
> 
> let currentLocale = Locale(identifier: "en_US")
> 
> let calendar1 = currentLocale.calendar      // "gregorian (fixed)"
> 
> let propertyName = "calendar"
> let calendar2 = currentLocale.propertyName // Error: Value of type 'Locale' has no member 'porpertyName'
> In the last line of code above, the instance of Locale thinks I am passing it "propertyName" rather than the contents of the variable "calendar".
> 
> Is there any way to pass the value of propertyName ("calendar") to the instance of Locale? I know that in other languages, you can prepend the variable name like '$propertyName', and that tells it to read the value of the variable.
> 
> I want to keep this pure Swift if possible.
> 
> I posted this question on StackOverflow, and got the following that does work:
> 
> let calendar2 = 
>     (currentLocale as NSLocale).object(forKey:NSLocale.Key(rawValue:propertyName))
> It does seem odd to me that we must do some crazy Objective-C gymnastics to make it work. It  would seem logical to have a computed property on the Any type named, let's say, contentsOf that would return or pass the contents of the variable to the called function. For example, to use the original code sample above, we could use:
> 
>     let calendar2 = currentLocale.propertyName.contentsOf
> 
> or something similar. Thus currentLocale.propertyName would pass the literal "propertyName", whereas currentLocale.propertyName.contentsOf would pass the contents "calendar".
> 
> Does anyone else agree that we need this functionality, or am I way out in left field on this? Or is this already possible and I haven't yet figured it out?
> 
> Sincerest Regards,
> Michael
> 
> Michael Sheaver
> msheaver at me.com <mailto:msheaver at me.com>
> 
> 
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org <mailto:swift-users at swift.org>
> https://lists.swift.org/mailman/listinfo/swift-users <https://lists.swift.org/mailman/listinfo/swift-users>
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-users/attachments/20160907/2c01f949/attachment.html>