explicit keyword

quote:

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Original post by Darkor
They say the explicit keyword is compiler specific. It prevents assignments during initilisation eg.

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They are wrong. Explicit keyword is a standard c++ keyword.

quote:

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Original post by Darkor
I''ve read in another article somewhere that another way to prevent this is to put the copy constructor and overloaded assignment operator in private.

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Provide a copy constructor and an assignment operator if the default copy semantics do not apply. Make them private if you want to disable copy semantics. Otherwise, there''s no other rule to follow IMO.

On a side note, you might want to look into the boost::non_copyable. It is basically an empty class that makes its copy and private assignment operator private. It actually makes your class copy semantics clearer, then making your own private operators.

There is a small difference between

trzGUI gui = anotherGUI;

and

trzGUI gui(anotherGUI);

Which may be what the thing you read was referring to.

trzGUI gui = anotherGUI; requires an implicit conversion if anotherGUI is not of type trzGUI.

trzGUI gui(anotherGUI); on the other hand, is treated as an EXPLICIT conversion from the type of anotherGUI to type trzGUI.

What does this all mean? Well the explicit keyword prevents a single argument constructor that it is applied to from doing implicit conversions.

So for instance if your class looked like this

class trzGUI
{
...
trzGUI( int i);
...
};

trzGUI gui = 1; //this is legal

however if your class uses the explicit keyword

class trzGUI
{
...
explicit trzGUI( int i);
...
};

trzGUI gui = 1; //this is NOT legal as it requires an implicit conversion.

trzGUI gui(1); //this is legal even when the constructor is declared explicit, as it is treated as an explicit conversion.

Ah kay, so things are cleared up then. By using explicit constructors, private copy constructors and assignment operators I blocked out all the holes then?

I''m not that particular though I believe in pragmatic programming, so this might help without being too much of a hassle.