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C++ create a class with array members which are not constructed.

From: Steve Hearnden <steve_at_[hidden]>
Date: Wed, 2 Sep 2020 19:44:54 +0100
I was looking at a performance issue, with some code and found that the cost of creating the dynamic heap memory was the significant cost.

It would have been handy to have a class which implemented something like std::vector, but with a *small* buffer of values to use as an alternative piece of memory when the vector size was below a threshold.
Unfortunately, an array of the constructed type, would cause the constructor to be called for each array element, and for complex types, could undo the benefit of the pre-bought memory.

My proposal would be for classes (or structures) to have the ability for a member to be declared with an attribute

which would cause none of the constructors to actually construct the object.
The class would not naturally also call destructors.

template< class T, size_t size>
class temp_vector
 [[unconstructed]] T _V[size];
 size_t m_constructed = 0;
///// Destroy the array manually.
  for( size_t i = 0; i < m_constructed; i++ ){

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Received on 2020-09-02 13:49:38