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Platform/Memory Reporting: Difference between revisions
→An Example Involving Inheritance
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=== An Example Involving Inheritance === | === An Example Involving Inheritance === | ||
Things are a little trickier when inheritance is involved. Every sub-class needs to have its own implementation of <tt>SizeOfExcludingThis</tt>. | Things are a little trickier when inheritance is involved. Every sub-class needs to have its own implementation of <tt>SizeOfExcludingThis</tt>. An example: | ||
class B { | class B { | ||
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{ | { | ||
size_t n = B::SizeOfExcludingThis(aMallocSizeOf); | size_t n = B::SizeOfExcludingThis(aMallocSizeOf); | ||
n += ... // measure D-specific fields | n += ... // measure things pointed to by D-specific fields | ||
return n; | |||
} | } | ||
}; | }; | ||
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* The <tt>NS_MUST_OVERRIDE</tt> is an annotation that indicates that this function must be overridden by any sub-classes. It's used by some static analysis tools. Currently these tools aren't running, but they might in the future, and it's a useful piece of documentation. | * The <tt>NS_MUST_OVERRIDE</tt> is an annotation that indicates that this function must be overridden by any sub-classes. It's used by some static analysis tools. Currently these tools aren't running, but they might in the future, and it's a useful piece of documentation. | ||
* The <tt>MOZ_OVERRIDE</tt> annotation says that <tt>D::SizeOfExcludingThis</tt> overrides the corresponding function in <tt>B</tt>. On supporting compilers it gets expanded to the <tt>override</tt> keyword. It | * The <tt>MOZ_OVERRIDE</tt> annotation says that <tt>D::SizeOfExcludingThis</tt> overrides the corresponding function in <tt>B</tt>. On supporting compilers it gets expanded to the <tt>override</tt> keyword. It helps prevent accidentally having small differences in the function signatures (e.g. forgetting a <tt>const</tt>) that prevent the overriding from happening. | ||
* The definitions of <tt>SizeOfIncludingThis</tt>, if needed, are straightforward and like the ones above. | * The definitions of <tt>SizeOfIncludingThis</tt>, if needed, are straightforward and like the ones above. | ||