Re: Constructor question...
On Tuesday, February 19, 2013 7:40:28 PM UTC, Tobias M=FCller wrote:
Anand Hariharan <mailto.anand.hariharan@gmail.com> wrote:
On Feb 13, 6:30 am, Tobias M=FCller <trop...@bluewin.ch> wrote:
Andy Champ <no....@nospam.invalid> wrote:
On 13/02/2013 02:20, Luca Risolia wrote:
Anyway, see if A a(cond ? x : y) works for you.
This assumes that there is only one constructor for A.
That's exactly what the OP said.
The expression involving ternary operator requires that 'x' and 'y' be
of the same type.
That's not quite true. One of them has to be convertible to the type of t=
he
other.
That's not quite true either (although it is close enough for
most use). More precisely, one of them has to be implicitly
convertible to the type of the other, *or* one of them must be a
throw expression.
One of the most frustrating consequences of this rule is that:
Base* pb = cond ? new Derived1 : new Derived2;4
doesn't work.
Since A has only one constructor, they have to be convertible to a common
type (let's call it Z) anyway. That means, with an appropriate cast on
either x or y, the ternary operator is perfectly suitable for any possibl=
e
combination of x, y and Z.
There's nothing in the original question which indicates whether
the constructor called should be the same or not. If the
constructor ultimately called should be the same.
A a( cond ? x : y );
, possibly with explicit conversions, is fine. Otherwise, if
the class supports copy:
A a ( cond ? A( x ) : A( y ) );
Otherwise, something like:
A const& a = cond ? A( x ) : A( y );
might work, but only for a const reference.
If none of the above work, then the OP will have to use:
std::unique_ptr<A> aptr( cond ? new A( x ) : new A( y ) );
A& a = *aptr;
Unless A is very simple, the cost of the extra allocation is
probably not significant.
--
James