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// Another error! Cannot extend

// a class marked as sealed!

class MyString

: String

{}

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U N D E R S TA N D I N G   I N H E R I TA N C E  A N D   P O LY M O R P H I S M

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8849CH06.qxd  10/1/07  10:35 AM  Page 188

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Note

In Chapter 4 you learned that C# structures are always implicitly sealed (see Table 4-3). Therefore, you

can never derive one structure from another structure, a class from a structure or a structure from a class.

As you would guess, there are many more details to inheritance that you will come to know

during the remainder of this chapter. For now, simply keep in mind that the colon operator allows

you to establish base/derived class relationships, while the sealed keyword prevents inheritance

from occurring.