When Initialization Lists shall not be used?

[pasa_1]

Can someone clarify few items from FAQ
http://www.parashift.com/c++-faq-lit....html#faq-10.6

'[10.6] Should my constructors use "initializa tion lists" or
"assignment "?'

a. This might happen when your class has two constructors that need to
initialize the 'this' object's data members in different orders. <--
Okay

b. Or it might happen when two data members are self-referential. <--
Can someone clarify this?

c. Or when a data-member needs a reference to the this object, and you
want to avoid a compiler warning about using the this keyword prior to
the { that begins the constructor's body (when your particular compiler
happens to issue that particular warning). ?? An example will be
helpful.

d. Or when you need to do an if/throw test on a variable (parameter,
global, etc.) prior to using that variable to initialize one of your
this members. ?? An example will be helpful.

Regards,
Manish

[Victor Bazarov]

pasa_1 wrote:

Can someone clarify few items from FAQ
http://www.parashift.com/c++-faq-lit....html#faq-10.6

'[10.6] Should my constructors use "initializa tion lists" or
"assignment "?'

a. This might happen when your class has two constructors that need to
initialize the 'this' object's data members in different orders. <--
Okay

b. Or it might happen when two data members are self-referential. <--
Can someone clarify this?

Not sure what's meant here, but if 'plast' needs to point to the last
element of a dynamically allocated array, you can either reoder the
members and initialise plast in the initialiser list or use assignment
like here:

struct A {
int *plast;
int n;
int *p;
A(int nn) : n(nn), p(new int[nn]) { plast = p[n-1]; }
};

c. Or when a data-member needs a reference to the this object, and you
want to avoid a compiler warning about using the this keyword prior to
the { that begins the constructor's body (when your particular
compiler happens to issue that particular warning). ?? An example
will be helpful.

struct A {
A* self;
A() : self(this) {} // can get a warning about use of 'this'
A(int) { self = this; } // no warning
};

d. Or when you need to do an if/throw test on a variable (parameter,
global, etc.) prior to using that variable to initialize one of your
this members. ?? An example will be helpful.

'throw' is a statement, and IIRC has to be in the body. OTOH, I am
not sure it cannot be circumvented with a static member function in
which you could both check and throw (and return the value to boot)...

V
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