Are these assignments on same pattern?

Question

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Shortcut for constructor

Are the following pieces of code the same in C++:

Piece1:

MyFunnyClass o = MyFunnyClass();

Piece2:

MyFunnyClass o;

I am aware that the following is not equivalent, but I am not sure about the two on the top:

MyFunnyClass o = MyFunnyClass () ;

MyFunnyClass o;
o = MyFunnyClass();

Wish I understood what exactly are you comparing to what ;-) — Michael Krelin - hacker, Sep 17 '12 at 17:36
This is not *really* a duplicate of that question, although it is related. The question marked as duplicate deals with *copy-initialization* vs. *direct-initialization*, while in this case it is *default-initialization* vs. *copy-initialization*. — David Rodríguez - dribeas, Sep 17 '12 at 19:19

Puppy · Accepted Answer · 2012-09-17T21:06:56.073

2

MyFunnyClass o () ;

This does not define an object in any way at all. This is the Most Vexing Parse. o is a function which takes nothing and returns a MyFunnyClass, which you have declared.

The real syntax would be

MyFunnyClass o;

This would default-construct an object.

MyFunnyClass o = MyFunnyClass();

Value-constructs an object and then copies or moves it into o. Expect ellision here.

edited Sep 17 '12 at 21:06

answered Sep 17 '12 at 17:42

Puppy

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This is missing the most important bit of information: *default* vs. *value* initialization. The last case is *value* initialization, not *default* initialization – David Rodríguez - dribeas Sep 17 '12 at 19:20
Good shout David, I'd forgotten about that. – Puppy Sep 17 '12 at 21:07

Are these assignments on same pattern?

1 Answers1