Michael Van Canneyt wrote:
On Sun, 22 Apr 2012, Mark Morgan Lloyd wrote:
cobines wrote:
2012/4/22 Mark Morgan Lloyd <markmll.fpc-pas...@telemetry.co.uk>:
but I'm not sure why that works when it
didn't earlier (i.e. before I'd started using array of const).
You said you used
DbgArray= array of integer
then I assume this declaration?
procedure ClrDebug(const panels: DbgArray);
If so the parameter is a dynamic array not open array and you cannot
call it with constant array:
var
arr: DbgArray;
begin
ClrDebug([DbgKey, DbgCode1, DbgTx]); //Won't work
SetLength(arr, ...);
arr[0] := ...
...
ClrDebug(arr);// This works
end;
This on the other hand is an open array parameter:
procedure ClrDebug(const panels: array of integer);
Thanks, succinct. So if I understand this correctly it's one of the
very rare cases where one has to write out the type of a parameter in
full, rather than using an earlier declaration.
It results in different declarations.
type
DbgArray = array of integer;
procedure ClrDebug(const panels: DbgArray);
Defines a procedure that accepts a dynamic array of type DbgArray.
You cannot have "constant dynamic arrays", as they are managed on the
heap and reference counted.
On the other hand
procedure ClrDebug(const panels: array of integer);
Defines a procedure that accepts an open array: an array of integers,
but without length. It accepts types as
type
SmallArray = array[1..100] of integer;
LargeArray = array[1..10000] of integer;
And a constant array (and a dynamic array, if I'm correct) as well.
I'll see if I can add something about it in the docs.
Hopefully Google will pick this up as a guide for the perplexed :-)
So if I understand things correctly, the important point here is that
while it is good practice to do e.g.
type dbgArray3= array[0..2] of integer;
procedure clrDebug3(da: dbgArray3);
rather than
procedure clrDebug3(da: array[0..2] of integer);
you quite simply can't do that when there isn't an explicit index range
since your attempt to define an open array is interpreted as a dynamic
array.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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