Beautiful Perl feature : fat commas, a device for structuring lists

Beautiful Perl series This post is part of the beautiful Perl features series. See the introduction post for general explanations about the series. Today's topic is a Perl construct called fat comma , which is quite different from the trailing commas discussed in the last post . Fat comma: an introduction A fat comma in Perl is a construct that doesn't involve a typographic comma! Visually it consists of an expression followed by an arrow sign => and another expression. This is used in many contexts, the most common being for initializing hashes or for passing named parameters to subroutines: my %rect = ( x => 12 , y => 34, width => 20, height = > 10 ); draw_shape ( kind => ' rect ', coords => \ %rect , color => ' green '); A fat comma is semantically equivalent to a comma; the only difference with a regular comma is purely syntactic : if the left-hand side is a string that begins with a letter or underscore and is composed only of letters, digits and underscores, then that string does