Нужны ли public конструкторы?

A C++ object's lifetime begins only after its constructor completes successfully. Therefore throwing an exception from a constructor always means (and is the only way of reporting) that construction failed. There is no way to recover from failed construction of a base or member subobject, so if construction of any base or member subobject fails, the whole object's construction must fail.

Avoid function try blocks, not because they're evil but just because they offer few or no benefits over plain try blocks — and when you're hiring you'll find that more people understand the latter than understand the former. This follows the principles of picking the simplest solution that's effective, and of writing for clarity first. Constructor function try blocks are useful only to translate exceptions emitted from base or member constructors, and all other function try blocks are rarely if ever useful at all.

 

1.  
2. class A
3. {
4. };
5.  
6. class B : public A
7. {
8. };
9.  
10. class Factory
11. {
12. public:
13.   A* MakeA( ... );
14.   B* MakeB( ... );
15. }

1.  
2. class A
3. {
4. };
5.  
6. class B : public A
7. {
8. };
9.  
10. class C : public B
11. {
12. };
13.  
14. class Factory
15. {
16. public:
17.   A* MakeA( ... );
18.   B* MakeB( ... );
19.   C* MakeC( ... );
20. }