Why Are There No Constructors in std::array to Assign a Specified Value to All Elements?

Constructor Limitations of std::array

Question:

Why doesn't std::array provide a constructor that initializes all elements with a specified value?

Answer:

By design, std::array is an aggregate type, which means it has no user-defined constructors. As a result, it cannot have a constructor like:

<code class="cpp">std::array<T, size>::array(const T& value);</code>

Alternatives:

Although std::array lacks such a constructor, there are alternative options to achieve the same result:

1. Default Construction and std::fill: After default constructing an std::array, you can use the std::fill function to assign a specific value to all elements:

   <code class="cpp">std::array<int, 10> arr;
   std::fill(arr.begin(), arr.end(), -1);</code>

2. Trivial Initialization and std::uninitialized_fill: If the type contained within the std::array is trivially initializable, default construction won't initialize the memory to zero but will leave it uninitialized. In such cases, you can use std::uninitialized_fill to assign a specific value to all uninitialized elements:

   <code class="cpp">std::array<std::string, 10> arr = {}; // Trivial initialization
   std::uninitialized_fill(arr.begin(), arr.end(), std::string("Example"));</code>

By understanding the limitations of std::array's constructors and employing these alternatives, you can effectively initialize all elements of an std::array with a desired value.

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