Re: [fpc-pascal] Pass open array to static array?
I just came across another related issue to this thread. Is it not possible to init dynamic arrays from static arrays? I remember there being more compatibility between the 2 types but I may have forgotten. var a: array[0..1] of integer; d: array of integer; begin d := a; end. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
Ryan Joseph via fpc-pascal schrieb am Fr., 3. Apr. 2020, 21:03: > > > > On Apr 3, 2020, at 10:09 PM, Sven Barth > wrote: > > > > If your DoThis would be declared with a dynamic array parameter (e.G. > "specialize TArray") 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 ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
> On Apr 3, 2020, at 10:09 PM, Sven Barth wrote: > > No. The "[...]" for an open array parameter means "open array constructer" > *not* "dynamic array constructor". And this on-the-fly open array is in fact > constructed on the stack. Ok, I see now. Excellent. I thought this was another dynamic array being created and destroyed. > > If your DoThis would be declared with a dynamic array parameter (e.G. > "specialize TArray") 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. 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. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
Ryan Joseph via fpc-pascal schrieb am Fr., 3. Apr. 2020, 14:33: > > > > > On Apr 3, 2020, at 3:43 PM, Sven Barth > wrote: > > > > They are neither. They are simply a pointer to the first element and a > hidden size argument. For the pointer it is not important where it comes > from: a single element, a dynamic array, a static array. > > > > Ah, I see. In the example below the open array is still a dynamic array > right? As you said earlier dynamic arrays are never constant/static (for > now at least) and therefore [1,2,3] is a dynamic. > > procedure DoThis(a: array of integer); > ... > DoThis([1,2,3]); > No. The "[...]" for an open array parameter means "open array constructer" *not* "dynamic array constructor". And this on-the-fly open array is in fact constructed on the stack. If your DoThis would be declared with a dynamic array parameter (e.G. "specialize TArray") 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. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
> On Apr 3, 2020, at 3:43 PM, Sven Barth wrote: > > They are neither. They are simply a pointer to the first element and a hidden > size argument. For the pointer it is not important where it comes from: a > single element, a dynamic array, a static array. > Ah, I see. In the example below the open array is still a dynamic array right? As you said earlier dynamic arrays are never constant/static (for now at least) and therefore [1,2,3] is a dynamic. procedure DoThis(a: array of integer); ... DoThis([1,2,3]); Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
Ryan Joseph via fpc-pascal schrieb am Fr., 3. Apr. 2020, 04:13: > > > > On Mar 16, 2020, at 5:40 AM, Sven Barth > wrote: > > > > The message of the compiler is a bit misleading. It's a *dynamic* array > that is created there, not an *open* array. Open arrays only exist when > being passed directly to a parameter. > > I forgot to ask. Are open arrays constants, or are they essentially > dynamic arrays also? > They are neither. They are simply a pointer to the first element and a hidden size argument. For the pointer it is not important where it comes from: a single element, a dynamic array, a static array. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
> On Mar 16, 2020, at 5:40 AM, Sven Barth wrote: > > The message of the compiler is a bit misleading. It's a *dynamic* array that > is created there, not an *open* array. Open arrays only exist when being > passed directly to a parameter. I forgot to ask. Are open arrays constants, or are they essentially dynamic arrays also? Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
Ryan Joseph via fpc-pascal schrieb am Mo., 16. März 2020, 07:33: > Ok, that makes sense now. Dynamic arrays can't be passed to static arrays. > I > remember when I tried to make aligned dynamic arrays I got to look around > in > the code and it seems plausible you could just make a memcpy call in the > RTL > for dynamic arrays being passed to static arrays. Seems deceptively easy. > :) > You forget managed types. You can't do a simple Move for them. > Shouldn't it be a constant array though? I'm not sure how the compiler > works > but from the programers perspective I thought I was getting something > without runtime allocation because the array contained only constant > values. > It's only a constant array if it's declared in the const section. Inside normal code it can also contain variables, function calls, just any expression really. Though it would be a potential optimization if all entries are constant to treat it as a constant array. Again that is something that *could* be done, but is not right now. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
Ok, that makes sense now. Dynamic arrays can't be passed to static arrays. I remember when I tried to make aligned dynamic arrays I got to look around in the code and it seems plausible you could just make a memcpy call in the RTL for dynamic arrays being passed to static arrays. Seems deceptively easy. :) Shouldn't it be a constant array though? I'm not sure how the compiler works but from the programers perspective I thought I was getting something without runtime allocation because the array contained only constant values. -- Sent from: http://free-pascal-general.1045716.n5.nabble.com/ ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
Ryan Joseph via fpc-pascal schrieb am So., 15. März 2020, 19:58: > > > > On Mar 15, 2020, at 8:53 PM, Howard Page-Clark via fpc-pascal < > fpc-pascal@lists.freepascal.org> wrote: > > > > > > With recent FPCs you can however do this: > > > > program test; > > var > > data: array[0..2] of Integer; > > tmp: array of Integer = Nil; > > begin > > tmp := [1,2,3]; > > Move(tmp[0], data[0], SizeOf(data)); > > end. > > yeah I figured you can do something similar with generics: > > generic procedure Move(source: array of T; var dest); > var > bytes: SizeInt; > begin > bytes := length(source) * sizeof(T); > Move(source, dest, bytes); > end; > > begin > specialize Move([0.0, 0.5, 0.0, > -0.5, -0.5, 0.0, > 0.5, -0.5, 0.0], > data.verts); > end. > > but why doesn't open arrays already do this? an open array is just a > constant array so the compiler should know the arrays are compatible for > assignments. > The message of the compiler is a bit misleading. It's a *dynamic* array that is created there, not an *open* array. Open arrays only exist when being passed directly to a parameter. But to answer why the compiler does not do it: because I simply have not had the time to implement it! The main point of dynamic array constructors was to have them Delphi compatible. Support for static arrays is something I have planned though (and you're not the first to ask for it). Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
> On Mar 15, 2020, at 8:53 PM, Howard Page-Clark via fpc-pascal > wrote: > > > With recent FPCs you can however do this: > > program test; > var > data: array[0..2] of Integer; > tmp: array of Integer = Nil; > begin > tmp := [1,2,3]; > Move(tmp[0], data[0], SizeOf(data)); > end. yeah I figured you can do something similar with generics: generic procedure Move(source: array of T; var dest); var bytes: SizeInt; begin bytes := length(source) * sizeof(T); Move(source, dest, bytes); end; begin specialize Move([0.0, 0.5, 0.0, -0.5, -0.5, 0.0, 0.5, -0.5, 0.0], data.verts); end. but why doesn't open arrays already do this? an open array is just a constant array so the compiler should know the arrays are compatible for assignments. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Pass open array to static array?
On 15/03/2020 12:06, Ryan Joseph via fpc-pascal wrote:
program test;
var
data: array[0..2] of integer;
begin
// Incompatible types: got "{Array Of Const/Constant Open} Array of ShortInt" expected
"Array[0..2] Of LongInt"
data := [1,2,3];
end.
With recent FPCs you can however do this:
program test;
var
data: array[0..2] of Integer;
tmp: array of Integer = Nil;
begin
tmp := [1,2,3];
Move(tmp[0], data[0], SizeOf(data));
end.
___
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