On 16.02.2011 11:03, Michael Engelhardt wrote:
Hi,
I just have started diving in D. Exploring the contract feature I
stumbled upon the fact that a class invariant does not apply to properties:
Welcome on board :)
Invariant gets called on every public method call (at begin & end if I'm
not mistaken).
Now to properties, this is actually shouldn't be allowed:
@property int hours;
@property is a annotation applied to functions (getter/setter), to allow
calling it with omitted () and a natural assign syntax like this:
class Time {
private:
int _hours;
public:
//...
@property int hours() {
return _hours;
}
@property void hours(int newHours) {
_hours = newHours;
}
}
auto t = new Time();
t.hours = 5; // calls void hours(5)
assert(t.hours == 5); //calls int hours()
Now given that setter and getter are public methods they'd got the invariant
called.
import std.stdio;
void main(string[] args) {
Time t = new Time();
t.hours = 24; // works; why?
writeln("t.hours is ", t.hours);
t.add(1); // triggers an assertion failure as expected
writeln("t.hours is ", t.hours);
}
class Time {
invariant() {
assert( 0<= hours&& hours< 13);
}
@property int hours;
public void add(int hours) {
this.hours += hours;
}
}
compiled using Digital Mars DMD (2.051 on Ubuntu 10.10) is given the
following result:
t.hours is 24
core.exception.AssertError@invarprop(13): Assertion failure
----------------
./InVariantProperty() [0x8057ade]
./InVariantProperty() [0x804f7e6]
./InVariantProperty() [0x804cba3]
./InVariantProperty() [0x8049856]
./InVariantProperty() [0x804fa86]
./InVariantProperty() [0x8049869]
./InVariantProperty() [0x8049813]
./InVariantProperty() [0x804f9f2]
./InVariantProperty() [0x804f94c]
./InVariantProperty() [0x804fa36]
./InVariantProperty() [0x804f94c]
./InVariantProperty() [0x804f8f4]
/lib/libc.so.6(__libc_start_main+0xe7) [0xa5cce7]
./InVariantProperty() [0x8049721]
Should not a class invariant apply to properties, too?
Kind regards
Michael
--
Dmitry Olshansky
