Mix everything up in a shaker, shake it up and pour over a tall glass filled with ice. Top up with sparkling water (soda water/club soda). I've had this served many a time, without the water, just enough ice to fill the glass up, which amounts to the same thing, just no fizz.
Singapore Sling Recipe 2 (Alex's)
Shake everything (not the pineapple slice) up in a shaker and pour into a glass, without ice. I love large Martini glasses for this.
Singapore Cricket Club Singapore Sling
Fill a small glass up with the ice cubes, pour all the ingredients over the ice, stir to mix and serve as is. Be warned, this is strong stuff!