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Comment by kleiba | Hacker News Reader

> It's the same as std::string product; product = "not worked";

Not a C++ person, so please forgive my ignorance, but what is the difference between the above and sth. like:

    std::string product = "not worked";

    std::string product("not worked");

(Are these even legal C++ statements and, if not, why not? ;-))

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Both are valid, and were the only ways of initializing objects before C++11, I think.

Brace initialization has an advantage in that it allows you to initialize compound values, like containers and structs, even if they're nested:

    std::map<int, std::string> m = { // nested list-initialization
           {1, "a"},
           {2, {'a', 'b', 'c'} },
           {3, s1}
    };

Ref: https://en.cppreference.com/w/cpp/language/list_initializati... https://en.cppreference.com/w/cpp/language/aggregate_initial...

I see, that's interesting.

How compile-time expensive is this? I guess it has to potentially consider a lot of constructor combinations?

it's also generally preferred because it can avoid certain narrowing conversions in construction: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines...

In practical terms, none. They are the same, and the same as using the curly braces.

From the POV of the standard, those are different kinds of initializations. C++ has like 12 different ways of initializing variables, and the differences are quite confusing, but in practical terms in my experience I never had to care too much beside making sure native types are initialized to some specified value.

You can probably find some talks on YouTube talking about the initializations of c++, and 1h30m is probably not enought to cover all the details :')

Yeah, that sounds like C++, I suppose. Thanks very much.

Thanks very much for the explanations, folks! One more follow-up question: what are reasons to prefer:

     std::string product; 
     product = "not worked";

i.e., separate declaration and initialization, as suggested by the grand-parent?

For this particular example direct initialization i.e. std::string product("not worked"); would be preferred, as you end up using one call to constructor instead of two: default constructor followed by the move assignment.

https://en.cppreference.com/w/cpp/language/direct_initializa... https://en.cppreference.com/w/cpp/language/move_assignment

Thank you very much.

What are examples of situations where the other pattern would be preferable?

afaik the only time you are really supposed to use uninitialized values is when you are planning on reading it in from some stream.

otherwise you should really avoid it.

Both are legal statements.

The second one is a direct initialization, invoking corresponding constructor.

The first one first invokes default constructor and then copy or move assignment depending on rvalueness of the arg.

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