On Tue, 24 Aug 2010 17:19:25 -0500, Andrej Mitrovic
<andrej.mitrov...@whatever.com> wrote:
[snip]
struct CheckedInt(N) if (isIntegral!N)
{
private N value;
this(N value)
{
this.value = value;
}
@property
auto Value()
{
return value;
}
// addition
CheckedInt opBinary(string op)(CheckedInt rhs) if (op == "+")
{
auto result = value + rhs.value;
enforce(rhs.value >= 0 ? result >= value : result < value);
return result;
}
}
I don't understand why he's trying to return result here (unless it was
a mistake). Result is going to have the type of "private N value",
whatever N may be, and this is conflicting with the return type which is
CheckedInt. So, this won't compile.
That's a bug. The return value should be CheckedInt(result);
He has the same returns for subtraction and multiplication, but for
others like division, shift and bitwise overload he has this:
// division and remainder
CheckedInt opBinary(string op)(CheckedInt rhs)
if (op == "/" || op == "%")
{
enforce(rhs.value != 0);
return CheckedInt(mixin("value" ~ op ~ "rhs.value"));
}
This looks correct. If I change the add overload from the code to this:
// addition
CheckedInt opBinary(string op)(CheckedInt rhs) if (op == "+")
{
auto result = value + rhs.value;
enforce(rhs.value >= 0 ? result >= value : result < value);
return CheckedInt(mixin("value" ~ op ~ "rhs.value"));
}
Then the return statement calls a CheckedInt constructor and I get back
a CheckedInt struct with the right value in the private variable "value".
What I don't understand is how the constructor can be called like that.
In my example the mixin would convert the code to:
return CheckedInt(10);
But if I ever tried a call like "CheckedInt(10)" in a unittest block, it
wouldn't work. So how does this magic work?
http://www.digitalmars.com/d/2.0/mixin.html
--
Yao G.
