C++ Object Initialization | Zack Yang’s Blog

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Why is Braced Initialization {} Generally Preferred?

As a general rule, initialization in C++ can be done with parenthesis, equal signs, or braces:

Braced initialization is also called uniform initialization. It is introduced in C++11 as a single initialization syntax that can be used anywhere and express everything. For example, before C++11, you couldn’t initialize a std::vector with a list of elements directly in its declaration. But after C++11, you can do this via braced initialization:.

Braces can also be used to specify default initialization values for non-static data members:

Moreover, braces can be used to initialize uncopiable objects:

This is why braced initialization is called uniform - among C++’s three ways to designate an initializing expression, only braces can be used everywhere.

extra features for braced initialization

it prohibits (禁止) implicit narrowing conversions among built-in types

it’s immune to C++’s most vexing parse

takeaways

braced initialization is the most widely usable initialization syntax, it prevents narrowing conversions, and it’s immune to C++’s most vexing parse

during constructor overload resolution, braced initializers are matched to std::initializer_list parameters if at all possible, even if other constructors offer seemingly better matches.

an example of where the choice between parentheses and braces can make a significant difference is creating a std::vector<numeric type> with two arguments

choosing between parentheses and braces for object creation inside templates can be challenging, because the template author sometimes does not know which initialization method is correct

general solution: choose one initialization method and document this decision as part of the interface.