Checking if a string has no special characters except for ".", "_" and "@"

Question

I'm currently writing a script which checks username & password validity. The username should have between 3 and 20 characters and no special characters, except for ".", "_" and "@".

Currently, this is my function:

fun isValidUsername(username: String): Boolean {
    var usrnmlength = true
    var usrnmspecial = true
    
    if ((username.length < 3) or (username.length > 20)) { usrnmlength = false }
    if (username.filter { !it.isLetterOrDigit() }.firstOrNull() != null) {usrnmspecial = false}

    return if ((usrnmlength) and (usrnmspecial)) {
        (true)
    } else {
        (false)
    }

}

It checks, if the username has between 3 and 20 characters and if the username has no special characters. But it also says that the username is not valid, if there are the special characters ".", "_" and "@". These should be allowed. How can I do this?

Answer 1

You can modify the condition for checking special characters to allow ".", "_", and "@" while filtering out other special characters. Here's the updated function:

fun isValidUsername(username: String): Boolean {
var usrnmlength = true
var usrnmspecial = true

if ((username.length < 3) or (username.length > 20)) { 
    usrnmlength = false 
}

if (username.filter { !(it.isLetterOrDigit() || it in listOf('.', '_', '@')) }.firstOrNull() != null) {
    usrnmspecial = false
}

return usrnmlength && usrnmspecial

}

This modification ensures that the username is considered valid if it has between 3 and 20 characters and contains only letters, digits, ".", "_", or "@".