Trimming strings in Scala

Question

How do I trim the starting and ending character of a string in Scala

For inputs such as \",hello\" or \"hello,\", I need the output as

Answer 1

Given you only want to trim off invalid characters from the prefix and the suffix of a given string (not scan through the entire string), here's a tiny trimPrefixSuffixChars function to quickly perform the desired effect:

def trimPrefixSuffixChars(
    string: String
  , invalidCharsFunction: (Char) => Boolean = (c) => c == ' '
): String =
  if (string.nonEmpty)
    string
      .dropWhile(char => invalidCharsFunction(char))  //trim prefix
      .reverse
      .dropWhile(char => invalidCharsFunction(char)) //trim suffix
      .reverse
  else
    string

This function provides a default for the invalidCharsFunction defining only the space (" ") character as invalid. Here's what the conversion would look like for the following input strings:

trimPrefixSuffixChars(" Tx  ")     //returns "Tx"
trimPrefixSuffixChars(" . Tx . ")  //returns ". Tx ."
trimPrefixSuffixChars(" T x  ")    //returns "T x"
trimPrefixSuffixChars(" . T x . ") //returns ". T x ."

If you have you would prefer to specify your own invalidCharsFunction function, then pass it in the call like so:

trimPrefixSuffixChars(",Tx. ", (c) => !c.isLetterOrDigit)     //returns "Tx"
trimPrefixSuffixChars(" ! Tx # ", (c) => !c.isLetterOrDigit)  //returns "Tx"
trimPrefixSuffixChars(",T x. ", (c) => !c.isLetterOrDigit)    //returns "T x"
trimPrefixSuffixChars(" ! T x # ", (c) => !c.isLetterOrDigit) //returns "T x"

This attempts to simplify a number of the example solutions provided in other answers.