cannot convert return expression of type 'String' to return type '(Int) -> String'

Question

it is normal working function :

func doSomeThing(productName : String , productPrice : Double)  -> String {

        return "good jobs"
    }

I might thinking function can take quantity parameter and return string

 func doSomeThing(productName: String , productPrice: Double) -> (Int) -> String{ 

     func totaPrice(quantity : Int) -> Double {

        return Double(quantity) * productPrice 

    }
   return "Product Name \(productName) each price is \(productPrice) , total price \(totaPrice)"
}

let totaPrice = doSomeThing(productName: "iPhone", productPrice: 649)
print(totaPrice(5))  
print(totaPrice(3)) 

But below error throwing :

ERROR at line 14, col 11: cannot convert return expression of type 'String' to return type '(Int) -> String' return "Product Name (productName) each price is (productPrice) , total price (totaPrice)" ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

how can fix this issue ?

Note :I want to do something like Currying function .

Solution 1

Your function header says you are returning a closure that takes an Int and returns a String, so that is what your function should return.

Here is an example that uses all of the inputs to construct the String:

func doSomeThing(productName: String, productPrice: Double) -> (Int) -> String {
    return { n in "\(n) \(productName)s cost \(productPrice * Double(n))" }
}

let iPhone = doSomeThing(productName: "iPhone", productPrice: 649)
print(iPhone(5))
print(iPhone(2))

Output:

5 iPhones cost 3245.0
2 iPhones cost 1298.0

Solution 2

I think the problem is you're trying to return twice in one method. Instead, just have your method take 3 parameters and return a String.

func doSomeThing(productName : String , productPrice : Double, quantity : Int) -> String {
    let total = productPrice * Double(quantity)
    return "The total for \(productName) is \(total)"
}

doSomeThing(productName: "my product", productPrice: 1.99, quantity: 1)

Comments

[Nazmul Hasan]

no sir ! i want to trying like Currying function .

[Nazmul Hasan]

well ! , are there no alternative way ?

[vacawama]

What is your objection with this way?

[Nazmul Hasan]

i want to make it simpler and sweeter .

[vacawama]

There isn't much wasted syntax in there. You can use $0 in place of n in the closure and get rid of n in, but I personally think its cleaner to explicitly name the parameter. Does this at least capture the functionality you were looking for?