Multiple Equatable functions in one class











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1
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I would like to know if its possible to have multiple Equatable functions in one class. My current problem is from this example:



class Ingredient: Equatable {

static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price
}

// static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
// return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price && lhs.quantity == rhs.quantity
// }
}


As you can see I would like to have commented equality function but it doesn't work this way because I already have one. I need both functions working. Is there any optimal solution for this?










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  • Optimal solution? The optional solution is to determine what uniquely identifies an object and use that when implementing Equatable and then use your own "specialised" functions for any other type of comparison, perhaps create a protocol to define them if they are to be implemented for several classes
    – Joakim Danielson
    Nov 11 at 15:02






  • 1




    How would that make any sense? Which function do you want Swift to use to determine equality? Either the quantity matters or it doesn't.
    – vacawama
    Nov 11 at 15:32















up vote
1
down vote

favorite












I would like to know if its possible to have multiple Equatable functions in one class. My current problem is from this example:



class Ingredient: Equatable {

static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price
}

// static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
// return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price && lhs.quantity == rhs.quantity
// }
}


As you can see I would like to have commented equality function but it doesn't work this way because I already have one. I need both functions working. Is there any optimal solution for this?










share|improve this question
























  • Optimal solution? The optional solution is to determine what uniquely identifies an object and use that when implementing Equatable and then use your own "specialised" functions for any other type of comparison, perhaps create a protocol to define them if they are to be implemented for several classes
    – Joakim Danielson
    Nov 11 at 15:02






  • 1




    How would that make any sense? Which function do you want Swift to use to determine equality? Either the quantity matters or it doesn't.
    – vacawama
    Nov 11 at 15:32













up vote
1
down vote

favorite









up vote
1
down vote

favorite











I would like to know if its possible to have multiple Equatable functions in one class. My current problem is from this example:



class Ingredient: Equatable {

static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price
}

// static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
// return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price && lhs.quantity == rhs.quantity
// }
}


As you can see I would like to have commented equality function but it doesn't work this way because I already have one. I need both functions working. Is there any optimal solution for this?










share|improve this question















I would like to know if its possible to have multiple Equatable functions in one class. My current problem is from this example:



class Ingredient: Equatable {

static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price
}

// static func == (lhs: Ingredient, rhs: Ingredient) -> Bool {
// return lhs.ingredientId == rhs.ingredientId && lhs.price == rhs.price && lhs.quantity == rhs.quantity
// }
}


As you can see I would like to have commented equality function but it doesn't work this way because I already have one. I need both functions working. Is there any optimal solution for this?







swift






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edited Nov 11 at 18:10









rmaddy

237k27308374




237k27308374










asked Nov 11 at 14:45









Marek Baláž

62




62












  • Optimal solution? The optional solution is to determine what uniquely identifies an object and use that when implementing Equatable and then use your own "specialised" functions for any other type of comparison, perhaps create a protocol to define them if they are to be implemented for several classes
    – Joakim Danielson
    Nov 11 at 15:02






  • 1




    How would that make any sense? Which function do you want Swift to use to determine equality? Either the quantity matters or it doesn't.
    – vacawama
    Nov 11 at 15:32


















  • Optimal solution? The optional solution is to determine what uniquely identifies an object and use that when implementing Equatable and then use your own "specialised" functions for any other type of comparison, perhaps create a protocol to define them if they are to be implemented for several classes
    – Joakim Danielson
    Nov 11 at 15:02






  • 1




    How would that make any sense? Which function do you want Swift to use to determine equality? Either the quantity matters or it doesn't.
    – vacawama
    Nov 11 at 15:32
















Optimal solution? The optional solution is to determine what uniquely identifies an object and use that when implementing Equatable and then use your own "specialised" functions for any other type of comparison, perhaps create a protocol to define them if they are to be implemented for several classes
– Joakim Danielson
Nov 11 at 15:02




Optimal solution? The optional solution is to determine what uniquely identifies an object and use that when implementing Equatable and then use your own "specialised" functions for any other type of comparison, perhaps create a protocol to define them if they are to be implemented for several classes
– Joakim Danielson
Nov 11 at 15:02




1




1




How would that make any sense? Which function do you want Swift to use to determine equality? Either the quantity matters or it doesn't.
– vacawama
Nov 11 at 15:32




How would that make any sense? Which function do you want Swift to use to determine equality? Either the quantity matters or it doesn't.
– vacawama
Nov 11 at 15:32












2 Answers
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No, you can not.



From the math definition of the function:




A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the codomain of the function.




In general, by defining more than one function with the same name which takes arguments of the same types you create ambiguity which leads to unpredictable results. So this behaviour will generate compile time error.






share|improve this answer






























    up vote
    1
    down vote













    You can't have multiple definitions of the ==() function (the function that gives you conformance to the equatable protocol) but you can write a complex implementation of your ==() function that uses more complex logic to decide how to compare two objects. You could even add a class variable to your class and have your ==() function use that variable in deciding how to compare values, although that seems like bad design.






    share|improve this answer





















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      2 Answers
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      active

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      2 Answers
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      up vote
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      No, you can not.



      From the math definition of the function:




      A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the codomain of the function.




      In general, by defining more than one function with the same name which takes arguments of the same types you create ambiguity which leads to unpredictable results. So this behaviour will generate compile time error.






      share|improve this answer



























        up vote
        2
        down vote













        No, you can not.



        From the math definition of the function:




        A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the codomain of the function.




        In general, by defining more than one function with the same name which takes arguments of the same types you create ambiguity which leads to unpredictable results. So this behaviour will generate compile time error.






        share|improve this answer

























          up vote
          2
          down vote










          up vote
          2
          down vote









          No, you can not.



          From the math definition of the function:




          A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the codomain of the function.




          In general, by defining more than one function with the same name which takes arguments of the same types you create ambiguity which leads to unpredictable results. So this behaviour will generate compile time error.






          share|improve this answer














          No, you can not.



          From the math definition of the function:




          A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the codomain of the function.




          In general, by defining more than one function with the same name which takes arguments of the same types you create ambiguity which leads to unpredictable results. So this behaviour will generate compile time error.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Nov 11 at 14:57

























          answered Nov 11 at 14:50









          fewlinesofcode

          1,928515




          1,928515
























              up vote
              1
              down vote













              You can't have multiple definitions of the ==() function (the function that gives you conformance to the equatable protocol) but you can write a complex implementation of your ==() function that uses more complex logic to decide how to compare two objects. You could even add a class variable to your class and have your ==() function use that variable in deciding how to compare values, although that seems like bad design.






              share|improve this answer

























                up vote
                1
                down vote













                You can't have multiple definitions of the ==() function (the function that gives you conformance to the equatable protocol) but you can write a complex implementation of your ==() function that uses more complex logic to decide how to compare two objects. You could even add a class variable to your class and have your ==() function use that variable in deciding how to compare values, although that seems like bad design.






                share|improve this answer























                  up vote
                  1
                  down vote










                  up vote
                  1
                  down vote









                  You can't have multiple definitions of the ==() function (the function that gives you conformance to the equatable protocol) but you can write a complex implementation of your ==() function that uses more complex logic to decide how to compare two objects. You could even add a class variable to your class and have your ==() function use that variable in deciding how to compare values, although that seems like bad design.






                  share|improve this answer












                  You can't have multiple definitions of the ==() function (the function that gives you conformance to the equatable protocol) but you can write a complex implementation of your ==() function that uses more complex logic to decide how to compare two objects. You could even add a class variable to your class and have your ==() function use that variable in deciding how to compare values, although that seems like bad design.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 11 at 14:56









                  Duncan C

                  91.5k13114194




                  91.5k13114194






























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