On 03/23/2011 06:48 AM, teo wrote:
How can I use properties with increment/decrement and +=/-= operators?
I did following tests (the errors are from dmd v2.052):
class T
{
private int _x;
@property
public int x() { return _x; }
}
void main()
{
int[] a;
// case #1.1
a.length++; // Error: a.length is not an lvalue
// case #1.2
a.length += 1; // Ok
auto t = new T();
// case #2.1
t.x++; // Error: t.x() is not an lvalue
// case #2.2
t.x += 1; // Error: 't.x' is not a scalar, it is a @property int()
// Error: incompatible types for ((t.x) += (1)):
'@property int()' and 'int'
// case #2.3
t.x()++; // Error: t.x() is not an lvalue
// case #2.4
t.x() += 1; // Error: t.x() is not an lvalue
}
Basically I want to change the value of a member variable, which is
accessed only through a property.
It looks like that is partially possible with the length property of
dynamic arrays although they probably are implemented in a different way.
You need a "write" property:
@property
{
public int x() { return _x; } // Read property
public void x(int x1) { _x = x1; } // Write property
}
As for the dynamic array length property:
void main()
{
int[] a;
++a.length; // Works
a.length += 1; // Works
a.length++; // Error: a.length is not an lvalue
}
I don't get why the error on a.length++ either. I'm curious about the
answer.
