Delphi and presumably Free Pascal has some language inconsistency and
problem/short coming concerning "Union Field" and/or "Union Property":
The (previous) presented solution (included at end of post) is inconsistent in
two ways:
1. Property of union not possible.
2. Order of field and property violations "field before property" rule.
(Both problems demonstrated in TDataExample3)
{
version 0.03 created on 14 august 2022 by Skybuck Flying:
Today I remember the rule which this union field is conflicting with.
The rule: "field before property"
Going to demonstrate it below
There are apperently two problems with this solution:
1. Property of union not possible ?!?
2. Inconsistent language design in respect to standard field + property relation
(order of appearance/declaration)
// ERROR "field definition not allowed after methods or properties" problem 2.
}
type
TDataExample3 = record
// mStandardField : integer; // OK
// normal/standard property
property StandardField : integer read mStandardField write
mStandardField;
mStandardField : integer; // ERROR "field definition not allowed
after methods or properties" problem 2.
// union property
// property UnionField : int64 read mData write mData; // not
possible, problem 1
// union fields
case integer of // INCONSISTENT problem 2
0 : ( mData : int64 );
1 : ( mByte : packed array[0..7] of byte );
// property UnionField : int64 read mData write mData; // not
possible, problem 1
end;
The original problem was:
(*
// ORIGINAL PROBLEM:
TDataExample0 = record
private
mField : integer;
public
// UNION example
case integer of
0 : ( mData : int64 );
1 : ( mByte : packed array[0..7] of byte );
property Field read mField write mField; // DOES NOT COMPILE.
end;
*)
// UNION DECLARATION example that does work without properties, just to
check"
TDataExample1 = record
private
mField : integer;
public
// UNION example
case integer of
0 : ( mData : int64 );
1 : ( mByte : packed array[0..7] of byte );
// DOES COMPILE
end;
Presented solution for union field in record with properties was:
TDataExample2 = record
private
mField : integer;
public
// SOLUTION:
property Field : integer read mField write mField;
// PUT CASE STATEMENT LAST
case integer of
0 : ( mData : int64 );
1 : ( mByte : packed array[0..7] of byte );
end;
Bye,
Skybuck.
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