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Feature
The Extends and Assigns Keywords
Issue: 2.1 (August/September 2003)
Author: Charles Yeomans
Author Bio: Charles Yeomans pontificates about most things REALbasic from his computer in Lexington, Kentucky.
Article Description: No description available.
Article Length (in bytes): 15,701
Starting Page Number: 21
RBD Number: 2111
Resource File(s):
2111.sit Updated: Friday, October 17, 2003 at 12:21 PM
Related Link(s): None
Known Limitations: None
Excerpt of article text...
REALbasic 5.1 introduced two new keywords, "Extends" and "Assigns," that allow developers to do wonderful things. In this article, we'll explore their use by way of examples, and also take a look at the benefits of their introduction for application design in REALbasic.
The Extends Keyword
The "Extends" keyword allows you to add new subroutines and functions to an existing class. It does this by telling the compiler to treat global methods as methods of the declared type of the first parameter. Some examples will make this clear.
Examples
As our first example, let's add a HexDump function to the MemoryBlock class.
Function HexDump(Extends m as MemoryBlock) as String
dim i, N as Integer
dim output as String
N = m.Size - 1
For i = 0 to N
If m.byte(i) < -at-h0A then
output = output + "0" + Hex(m.byte(i))
Else
output = output + Hex(m.byte(i))
End if
Next
Return output
End Function
In the declaration of HexDump, the presence of the keyword "Extends" in front of the MemoryBlock parameter tells RB that HexDump should not be treated as a global function anymore. Instead, it can and must be called as a function of the MemoryBlock class.
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Article copyrighted by REALbasic Developer magazine. All rights reserved.
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