[fpc-pascal] Pass open array to static array?
pascaldragon at googlemail.com
Sat Apr 4 10:08:20 CEST 2020
Ryan Joseph via fpc-pascal <fpc-pascal at lists.freepascal.org> schrieb am
Fr., 3. Apr. 2020, 21:03:
> > On Apr 3, 2020, at 10:09 PM, Sven Barth <pascaldragon at googlemail.com>
> > 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:
MyArray: array of LongInt = (1, 2, 3);
If the writable constants switch is off then this dynamic array won't be
> 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
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
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
SomeFunc(MyArrayArg[3..High(MyArrayArg) - 3]);
This will also work correctly with var/out open array parameters.
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