Who thought it was cool to be able to create partial classes without indicating on the 'primary' class that it has other parts somewhere else. In C# you must use the partial keyword on all parts, so why not VB?
Since partial type cannot span projects (i.e. a type must be fully described inside of a project), we felt it was sufficient to only have to have at least one of the declarations “opt in” to partialness. Requiring every partial declaration to have to specify that it was partial seemed to be unnecessarily strict. For example, in the designer case such as a WinForm, it is really necessary to put “Partial” on the class declaration when the partial type that the designer spits isn't even shown by default?
And, of course, there's no reason that a developer can't specify “Partial“ on all partial declarations if they so choose. You can even modify, say, the WinForms template to add it if you want.
In the end, this is one of those things I was talking about just last week, a real judgement call. There are more than a few people who have taken issue with this particular decision, feeling that the more explicit the better. (There have been even suggestions made to us that partial types should have to explicitly state which source file the other partial types reside.) I can see their point and don't think their arguments are bad, we just don't happen to agree on this...
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