If I remember correctly, keys are always treated like strings and can't be considered an integer, etc. With that in mind, just think of what you could do to a string and you should be all right. For example:

for($I=0;$I<3;$I++){
$foo{"word".$I}= "This is word $I\n";
}
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You could then reference foo with $foo{word0}, $foo{word1}, and $foo{word2}