[swift-users] overloading methods where only difference is optional vs. non-optional type

[C. Keith Ray]

You need to know that the NAME of a method or function isn't just outside the parenthesis.

The name of 

    func IsTextEmpty(foo : String?) -> Bool? 

is

    "IsTextEmpty(foo:)"

and the name of


    func IsTextEmpty(text : String?) -> Bool

is

    "IsTextEmpty(text:)"

The argument labels are important.


func IsTextEmpty(foo : String?) -> Bool? {
    return foo?.isEmpty
}

func IsTextEmpty(text : String?) -> Bool {
    guard let text = text else {
        return true
    }
    
    return text.isEmpty
}

print(IsTextEmpty(foo: "1"), IsTextEmpty(text: "2"))
// prints Optional(false) false


--
C. Keith Ray
Senior Software Engineer / Trainer / Agile Coach
* http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf



> On Oct 10, 2017, at 10:27 AM, C. Keith Ray <keithray at mac.com> wrote:
> 
> nope. it's the same as this example:
> 
> func funny() -> Int {
>  return 1
> }
> 
> func funny() -> String {
>  return "2"
> }
> 
> print(funny()) // the compiler doesn't know which one you want.
> 
> // the above doesn't compile.
> // error: forloop.playground:8:1: error: ambiguous use of 'funny()'
> 
> 
> You have to have some difference visible in the caller:
> 
> 
> func funny(useInt: Bool) -> Int {
>  return 1
> }
> 
> func funny(useString: Bool) -> String {
>  return "2"
> }
> 
> print(funny(useInt: true), funny(useString: true))
> // prints "1 2\n"
> 
> 
> --
> C. Keith Ray
> Senior Software Engineer / Trainer / Agile Coach
> * http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf <http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf>
> * https://leanpub.com/wepntk <https://leanpub.com/wepntk> <- buy my book?
> 
> 
>> On Oct 10, 2017, at 9:06 AM, Phil Kirby via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> 
>>  <>2 down vote <> favorite <https://stackoverflow.com/questions/46620311/overloading-methods-where-only-difference-is-optional-vs-non-optional-type#> 
>> Original StackOverflow post:
>> 
>> https://stackoverflow.com/questions/46620311/overloading-methods-where-only-difference-is-optional-vs-non-optional-type <https://stackoverflow.com/questions/46620311/overloading-methods-where-only-difference-is-optional-vs-non-optional-type>
>> I was under the impression that swift can have overloaded methods that differ only in the type of object that the methods return. I would think that I could have two funcs with the same signature yet they differ in return type.
>> 
>> import Foundation
>> 
>> // ambiguous use of 'IsTextEmpty(text:)'
>> func IsTextEmpty(text : String?) -> Bool? {
>>   return text?.isEmpty
>> }
>> 
>> func IsTextEmpty(text : String?) -> Bool {
>>    guard let text = text else {
>>      return true
>>    }
>> 
>>    return text.isEmpty
>> }
>> 
>> let text: String? = nil
>> 
>> if let empty = IsTextEmpty(text:"text") {
>>    print("Not Empty")
>> }
>> 
>> if IsTextEmpty(text: text) {
>>    print("Empty")
>> }
>> Here, both functions have the same input parameters but one func returns an optional Bool? and the other returns a Bool. In this case I get an error:
>> 
>> ambiguous use of 'IsTextEmpty(text:)'
>> If I change the name of one of the input parameters I no longer get the ambiguous error:
>> 
>> // Works
>> func IsTextEmpty(foo : String?) -> Bool? {
>>   return foo?.isEmpty
>> }
>> 
>> func IsTextEmpty(text : String?) -> Bool {
>>    guard let text = text else {
>>      return true
>>    }
>> 
>>    return text.isEmpty
>> }
>> 
>> let text: String? = nil
>> 
>> if let empty = IsTextEmpty(foo:"text") {
>>    print("Not Empty")
>> }
>> 
>> if IsTextEmpty(text: text) {
>>    print("Empty")
>> }
>> Shouldn't the compiler detect that they are two distinct methods even though their return types are different, since an optional Bool? is a different type from a non-optional Bool?
>> 
>> 
>> _______________________________________________
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>> swift-users at swift.org <mailto:swift-users at swift.org>
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> 

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