Built In Types: String

The string type, string, is used to represent a sequence of zero or more characters. Conceptually, a string can be considered as an array of characters -- the elements -- whose keys are the int values starting at zero. The type of each element is string. A string whose length is zero is an empty string.

A numeric string is a string containing the following: optional leading whitespace, followed by an optional sign, followed by a base-10 integer or floating-point number. A leading-numeric string is a string whose initial characters follow the requirements of a numeric string, and whose trailing characters are non-numeric. A non-numeric string is a string that is not a numeric string. For example:

""              // empty string
"Hello"         // string containing 5 characters
" -123"         // numeric string
'2e+5'          // numeric string

Consider the following example:

class Point {
  private float $x;
  private float $y;
  public function __construct(num $x = 0, num $y = 0) {
    $this->x = (float)$x;
    $this->y = (float)$y;
  }
  public function __toString(): string {
    return '('.$this->x.','.$this->y.')';
  }
  // ...
}

<<__EntryPoint>>
function main(): void {
  $p1 = new Point(1.2, 3.3);
  /* HH_FIXME[4067] implicit __toString() is now deprecated */
  echo "\$p1 = ".$p1."\n";
}
Output
$p1 = (1.2,3.3)

Method __toString has a return type of string. The return expression results in the concatenation of the three string literals and the two float property values into a single string.

'(', ',', ')', "\$p1 = ", and "\n" are examples of string literals.

Strings are usually manipulated with functions from the Str\ namespace in the Hack Standard Library.