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Language: Visual Basic
Expertise: Advanced
Jul 30, 1997
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Implementation of Public Forms and Class Variables
The implementation of Public variables in forms and classes changed with Visual Basic 5.0. VB4 implements
public variables in forms and class modules as if they're regular variables, using pointers to data in memory.
In VB5, public variables are more correctly implemented as a pair of hidden Get/Let property procedures.
This approach slows down these properties when the program is ported from VB4 to VB5.
More importantly, this change likely breaks any code that relies on passing such variables to procedures as
ByRef arguments and expects that the procedure modifies them. In fact, under VB5, they're passed by
value, and the original property is never affected. For more information on this issue, see article Q166928 in
the Microsoft Knowledge Base.
Francesco Balena
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