Associative Arrays in Shell Scripts

I saw a trick for implementing associative arrays in a shell script. For example print array["apples"] could be scripted as echo \$array$key where key=apples. However, there was no mention of how to generate the keys to iterate over the array. The only way I could think of was to store the keys in a variable delimited by spaces so I could use a for-loop to iterate over the array. So, is there some other way to store the keys for later use?