swift - SWIFT : warnings upon compilation but good behaviour

我正在使我的代码正常运行，除了警告是在编译时发出的事实之外，因为我自己学习，所以我真的不知道这些警告来自何处。如何修改代码(介于FIXME BEGIN和FIXME END之间)以使代码在没有警告的情况下进行编译？

代码:

protocol EqualsMethod {
    // Notice that the type-keyword  "Self" helps to solve the
    // curriously recurring interface pattern for direct self-reference
    // FIXME-begin
    func equality(my: Self) -> Bool;
    // FIXME-end
}

struct my_int : EqualsMethod {
    // FIXME-begin
    func equality(my: my_int) -> Bool{
        if (my.value == value){
            return true;
        }
        return false
    }
    // FIXME-end

    var value: Int;
}

// Returns the index of an element if it exists
// nil otherwise
func findIndex
    // FIXME-begin
    <T: EqualsMethod>
    // FIXME-end
    (valueToFind: T, array:[T]) -> Int? {

        // FIXME-begin
        for (k, e) in array.enumerated(){
            if (valueToFind.equality(my: e))
            {
                return k;
            }
        }
        // FIXME-end

        // Index not found
        return nil
}

let ints = [my_int(value: 1),
            my_int(value: 2),
            my_int(value: 3),
            my_int(value: 4),
            my_int(value: 5)]

print(findIndex(valueToFind: my_int(value: 2), array: ints))
print(findIndex(valueToFind: my_int(value: 0), array: ints))

预期输出:

Optional(1)
nil

警告:

main.swift:49:7: warning: expression implicitly coerced from 'Int?' to 'Any'
print(findIndex(valueToFind: my_int(value: 2), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.swift:49:7: note: provide a default value to avoid this warning
print(findIndex(valueToFind: my_int(value: 2), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                            ?? <#default value#>
main.swift:49:7: note: force-unwrap the value to avoid this warning
print(findIndex(valueToFind: my_int(value: 2), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                           !
main.swift:49:7: note: explicitly cast to 'Any' with 'as Any' to silence this warning
print(findIndex(valueToFind: my_int(value: 2), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                            as Any
main.swift:50:7: warning: expression implicitly coerced from 'Int?' to 'Any'
print(findIndex(valueToFind: my_int(value: 0), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.swift:50:7: note: provide a default value to avoid this warning
print(findIndex(valueToFind: my_int(value: 0), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                            ?? <#default value#>
main.swift:50:7: note: force-unwrap the value to avoid this warning
print(findIndex(valueToFind: my_int(value: 0), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                           !
main.swift:50:7: note: explicitly cast to 'Any' with 'as Any' to silence this warning
print(findIndex(valueToFind: my_int(value: 0), array: ints))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                            as Any

最佳答案

findIndex()返回Int?，然后print()将其强制为Any。

从警告开始，应用建议的修复程序之一:

print(findIndex(valueToFind: my_int(value: 2), array: ints) ?? -1) // one option
print(findIndex(valueToFind: my_int(value: 2), array: ints)!) // another option, may crash
print(findIndex(valueToFind: my_int(value: 2), array: ints) as Any) // third option