Mark Morgan Lloyd <markmll.fpc-pas...@telemetry.co.uk> schrieb am Do., 7. Juni 2018, 11:46:
> On 04/06/18 12:00, Nitorami wrote: > >>> It would be reasonable to assume that the predefined + might be>> > substantially more efficient than a programmer-defined one could be. > >> Yes, that's one of the reasons I vote for keeping the new feature>and > allow to overload the operator. > > I don't think that argument holds water. Concatenation of dynamic > structuresis a slow function in the first place. I am not a core developer, > but Iconsider that regardless how you do it, it will require a call to > setlength,which in turn will call the operating system to allocate memory > for the nowlarger structure. That takes much more time than a few assembly > instructionsfor a normal pascal procedure call. > > The obvious workaround is to preallocate a dynamic array to a nominal > size and then to trim it using SetLength(0), I'd assumed that it would > retain ownership of the memory but I've just checked. > > What actually happens is that the memory is released back to the heap > (but *not* to the OS, at least on Linux), with the result that > concatenating elements will introduce a substantial hit particularly if > space for a new element allocated from the heap isn't contiguous. > Of course SetLength(0) releases the memory as the value of a dynamic array with length 0 is Nil, so nothing can be saved there. Regards, Sven >
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