Type::Tiny is probably best known as a way of having Moose-like type constraints in Moo, but it can be used for so much more. This is the first in a series of posts showing other things you can use Type::Tiny for.

Let's imagine you have a function which takes three parameters, a colour, a string of text, and a filehandle. Something like this:

  sub htmlprint {
    my %arg = @_;
    $arg{file}->printf(
      '<span style="color:%s">%s</span>',
      $arg{colour},
      $arg{text},
    );
  }

Nice little function. Simple enough. But if people call it like this:

  htmlprint( file => $fh, text => "Hello world", color => "red" );

... then they'll get weird and unexpected behaviour. Have you spotted the mistake?