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QueryInterface
requires transitive and reflexive
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properties:
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nsCOMPtr<nsIFoo>
foo = do_CreateInstance(…);
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nsCOMPtr<nsIBar>
bar = do_QueryInterface(foo);
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nsCOMPtr<nsIFoo>
foo2 = do_QueryInterface(bar);
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//
guarantee is that foo == foo2
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InterfaceRequestor
does not follow this:
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nsCOMPtr<nsIFoo>
foo = do_CreateInstance(…);
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nsCOMPtr<nsIBar>
bar = do_GetInterface(foo);
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// these
calls may or may not fail, or may return different
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objects
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nsCOMPtr<nsIFoo>
foo2 = do_GetInterface(bar); // ??
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nsCOMPtr<nsIfoo>
foo3 = do_QueryInterface(bar); // ??
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