Ryan Joseph via fpc-pascal <fpc-pascal@lists.freepascal.org> schrieb am Fr., 3. Apr. 2020, 21:03:
> > > > On Apr 3, 2020, at 10:09 PM, Sven Barth <pascaldra...@googlemail.com> > wrote: > > > > If your DoThis would be declared with a dynamic array parameter (e.G. > "specialize TArray<Integer>") then you'd in fact have a temporary dynamic > array constructed on the heap. > > > > Also I didn't say that dynamic arrays can't be constant, but that they > only are so if declared in a const section. > > > > can you post an example of a const dynamic array? I tried and it thinks > it's a set so I can't assign to an open array. > It needs to be a typed constant: const MyArray: array of LongInt = (1, 2, 3); If the writable constants switch is off then this dynamic array won't be writable either. > Also that made me think, is it possible for an open array parameter to be > written to if its source was a static array? You said it's a pointer so I > wonder if it's possible to use them instead of passing a static array > pointer with an additional parameter for the length. > Yes that is indeed the case though you'll have to declare the parameter as var as otherwise the compiler will create a copy on the stack which will be lost afterwards. Also open array *always* start at index 0. So if you pass a static array that's declared as 4..6 then your function will get an open array stsrting at 0 with length 3 with the element at 0 being the element at 4 of the static array. And as a special functionality open arrays allow slicing. That is if you have an open array parameter you can pass along parts of it to another open array: SomeFunc(MyArrayArg[3..High(MyArrayArg) - 3]); This will also work correctly with var/out open array parameters. Regards, Sven
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