Is there a better way to check a string contains both number kotlinlang #codereview

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Title

Simon Lin

09/10/2021, 8:43 AM

Is there a better way to check a string contains both number and alphabet?

val text = "aas211w"
if (text.any { it.isDigit() } && text.any { it.isLetter() }) {
}

ephemient

09/10/2021, 8:56 AM

depends on what you want. note that (due to Char's 16-bit nature)

"Ｓ".any { it.isLetter() } == true
"𐐠".any { it.isLetter() } == false

Tobias Suchalla

09/10/2021, 10:21 AM

any

also only checks if at least one of the chars matches the predicate, I suspect you might want

all

val text = "aas211w"
if (text.all { it.isDigit() || it.isLetter() }) {
    // do something
}

Matteo Mirk

09/10/2021, 12:58 PM

val text = """aas211W𐐠Ｓ""" // contains UTF8 letters
text.matches("""[\p{L}\d]+""".toRegex()) // true, UTF8-inclusive

if you just need to match ASCII letters the regex becomes

"""[a-zA-Z\d]+"""

Klitos Kyriacou

09/10/2021, 1:42 PM

I was wondering what you meant by "contains UTF8 letters". A String doesn't normally contain UTF8, that's just an encoding scheme for converting bytes into ~~characters~~ code points. I presume you meant your source code contained UTF8 letters, but once parsed and stored in a String they are just Unicode letters.

Matteo Mirk

09/10/2021, 2:34 PM

Sorry, my mistake, I confused terms: I meant unicode letters outside of the ASCII range. I used the wrong word, the encoding in place of the code points.

brandonmcansh

09/11/2021, 6:10 PM

isn't there an

isLetterOrDigit()

in the JVM already?

Matteo Mirk

09/13/2021, 1:53 PM

there is an extension method in Kotlin SDK since 1.0:

fun Char.isLetterOrDigit(): Boolean

an yes, there are the static methods in the Char class •

public static boolean isLetterOrDigit(char ch)

since Java 1 •

public static boolean isLetterOrDigit(int codePoint)

since Java 5 good catch Brandon, I totally forgot those!

ephemient

09/14/2021, 5:49 PM

back to the original question… if the desire is to do something like those vexing password rules (must have a digit, must have a letter) then

.isLetterOrDigit()

doesn't help, but the original can be modified to be Unicode-safe on JVM:

"aas211w".codePoints()
    .map { if (Character.isDigit(it)) 1 else if (Character.isletter(it)) 2 else 0 }
    .reduce(0, Int::or) == 3

🙌 1

or if Java 8+ isn't available, something like

generateSequence(0) { offsetByCodePoints(it, 1) }.takeWhile { it < length }.map { codePointAt(it) }

instead of

.codePoints()

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