Florian Klaempfl wrote on Sun, 18 Oct 2009:
Jonas Maebe schrieb:
Florian Klaempfl wrote on Sat, 17 Oct 2009:
Graeme Geldenhuys schrieb:
Would you mind explaining this - I never saw the benefit of a sealed
class.
From a compiler developers point of view, it makes optimization easier
under certain cases (e.g. virtual method calls).
FPC can already do this automatically for all classes in the entire
program with whole-program optimization. You don't need sealed classes
for this (they might slightly improve those optimizations,
I made a mistake here: they can't improve it. Since such a class won't
be derived from even without the "sealed" specifier, the compiler can
perform all those optimizations automatically already.
but I doubt
it will be noticeable in real life -- even doing it for an entire
program using WPO generally has no noticeable effects on speed, and only
marginal effects on code size).
True. But sealed requires no recompilations to do the optimization, so
it works always.
Declaring a class as "sealed" for optimization purposes is a
micro-optimization that pollutes the source code. In that case, you'll
probably have to revert that change again later if you or someone else
does have to inherit from the class after all. It may also force
people into using delegation rather than inheritance, and this in turn
can cause problems if the sealed class is "unsealed" later on and new
descendants are created after all (e.g., because they directly created
a delegate of the "sealed" type since it couldn't be inherited from
anyway).
Manually doing things that can be automated is almost never a good idea.
Jonas
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