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"negative count" and unsigned counts

From: Darin Adler <darin@apple.com>
Date: 19 Sep 2003 13:16:13 -0400
Message-Id: <3D77D2A7-EAB8-11D7-A583-0003935B80A2@apple.com>
Cc: intrigue@group.apple.com
To: www-dom@w3.org




(The previous version had some confusing typos; this is a corrected 
message.)

Consider the interface CharacterData from DOM Level 1. The method 
deleteData has an unsigned long parameter named count. The technical 
report says that if the specified count is negative the exception 
INDEX_SIZE_ERR should be raised. But since count is an unsigned long, 
it makes no sense to say an exception should be raised if the count is 
negative; an unsigned long can't be negative.

In practice, this creates a problem for language binding implementors. 
For example, the W3C DOM test suite has an ECMAScript test that 
attempts to pass a negative number to deleteData, and expects 
INDEX_SIZE_ERR. But conceptually, it's the ECMAScript DOM language 
binding that is going to encounter the need to convert the negative 
number to an unsigned long, and I think it may be unreasonable to 
expect the language binding to know that it should raise a DOMException 
INDEX_SIZE_ERR in this case, since the process of converting argument 
types shouldn't be required to know details of individual DOM methods.

I was unable to find any standard that defines what should happen to 
values of inappropriate types that are passed through a language 
binding. I expect that's outside the scope of the DOM technical report.

There's definitely a problem here, but I'm not sure what can be done to 
the DOM technical report to fix this. Perhaps the idea of using 
unsigned long as the type in the CharacterData interface is the 
problem; it's certainly inconsistent to talk about a negative count if 
a count is an unsigned long.

This issue exists for the substringData, insertData, deleteData, and 
replaceData methods of the interface CharacterData, and the splitText 
method of the interface Text.

     -- Darin
Received on Friday, 19 September 2003 13:16:17 GMT

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