Swift String contain , or . but not both

Question

I want to write the following in a more elegant way:

let number = "1,2922.3"

if number.contains(",") || number.contains(".") && !(number.contains(".") && number.contains(",")) {
    // proceed
}

That is, I want to proceed if the number has "." or ",", but not them both.

There has to be a better way?

I don't want to use an extension, as this is in a single place in my code.

You should use an extension. Extensions are specifically for single places in your code. Always use an extension. (In some cases use a function instead, but generally an extension.) — Fattie, May 17 '21 at 19:10
@Fattie I don't think that was the intention. The OP is stating that don't want to add an extension as this is a one-time check only - they don't want to extend a class across the board *Extensions add new functionality to an existing class, structure, enumeration, or protocol type.* [Extension](https://docs.swift.org/swift-book/LanguageGuide/Extensions.html) — Jay, May 17 '21 at 19:17
Sometimes simpler is better! There's really nothing wrong with that code so it's not clear why you want to simplify it. Note there is a slight logic error in that you're want to group your OR together for evaluation as a group like this `( number.contains(",") || number.contains(".") ) && !( number.contains(".") && number.contains(",") )`. So that now reads the string contains ( . OR , ) AND does not contain both. That makes the first part to evaluate to true if , or . — Jay, May 17 '21 at 19:32
This seems suspiciously close to validating number formats. Your idea of a "correct format" is probably wrong, so tread carefully. — Alexander, May 17 '21 at 19:37

AnderCover · Accepted Answer · 2021-05-17T19:35:15.623

You can use SetAlgebra:

func validate(_ string: String) -> Bool {
    let allowed = Set(",.")
    return !allowed.isDisjoint(with: string) && !allowed.isSubset(of: string)
}

validate("1,2922.3") // false
validate("1,29223") // true
validate("12922.3") // true
validate("129223") // false

To explain a bit:

!allowed.isDisjoint(with: string) because you want to exclude strings that contain neither . and ,.
!allowed.isSubset(of: string) because you want to exclude strings that contain both . and ,.

Swift String contain , or . but not both

1 Answers1