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GNU Smalltalk User's Guide

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4.2.4 Smalltalk dictionary

If you'll remember from the beginning of the chapter, we started out by saying:
 
   Smalltalk at: #x put: 0 !

This code should look familiar--the at:put: message is how we've been storing information in our own arrays and dictionaries. In a Smalltalk environment the name Smalltalk has been preset to point to a dictionary (21) which both you and Smalltalk can use. To see how this sharing works, we'll first try to use a variable which Smalltalk doesn't know about:
 
   y := 0 !

Smalltalk complains because y is an unknown variable. Using our knowledge of dictionaries, and taking advantage of our access to Smalltalk's dictionary, we can add it ourselves:

 
   Smalltalk at: #y put: 0 !

The only mystery left is why we're using #y instead of our usual quoted string. This is one of those simple questions whose answer runs surprisingly deep. The quick answer is that #y and 'y' are pretty much the same, except that the former will always be the same object each time you use it, whereas the latter can be a new string each time you do so. (22)

Now that we've added y to Smalltalk's dictionary, we try again:
 
   y := 1 !
It works! Because you've added an entry for y, Smalltalk is now perfectly happy to let you use this new variable. If you have some spare time, you can print out the entire Smalltalk dictionary with:
 
   Smalltalk inspect !

As you might suspect, this will print out quite a large list of names! If you get tired of watching Smalltalk grind it out, use your interrupt key (control-C, usually) to bring Smalltalk back to interactive mode.


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