How to Choose the Right C 11 Initializer Syntax and When to Use Them?

The Dilemma of Initializer Syntax in C 11

With the introduction of C 11, developers gained a new set of syntax options for initializing classes, adding to the already existing brace-enclosed initializer. This plethora of choices has presented a puzzling dilemma: when to use each syntax option?

Defaulting to Copy Initialization

The provided guideline suggests that if the intent is to assign an exact value to an object, copy initialization (=) should be favored. This is because it minimizes the risk of inadvertently invoking an explicit constructor with potentially different semantics. Brace initialization should be considered if copy initialization is unavailable, and parentheses initialization should be used as a last resort.

Curly Braces for Bulk Initialization

Curly braces initialization excels when initializing with multiple values intended to be stored within the object. This syntax is particularly suitable for vectors, arrays, and complex numbers.

Parentheses for Descriptor Initialization

When the values provided during initialization describe the intended state or behavior of the object rather than its actual data, parentheses initialization should be employed. This is often the case with arguments specifying size or file names.

Example Application

Consider the following code snippets:

<code class="cpp">{ // Example 1
  int b(1); // Copy initialization for exact value
  int a{1}; // Brace initialization for stored value
  int c = 1; // Parentheses initialization for descriptor value (e.g., size)
  int d = {1}; // Brace initialization for stored value
}</code>

<code class="cpp">{ // Example 4
  std::function<int(int,int)> a(std::plus<int>()); // Copy initialization for callback function
  std::function<int(int,int)> b{std::plus<int>()}; // Brace initialization for callback function, likely unwanted
}</code>

By following the proposed guideline, developers can navigate the complexities of C 11 initializer syntax with confidence, ensuring their code is both accurate and efficient.

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