RFR: 8319117: GrowableArray: Allow for custom initializer instead of copy constructor

[Johan Sjölen]

On Sun, 29 Oct 2023 14:00:25 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi, 
> 
> When using at_put and at_put_grow you can provide a value which will be supplied to the constructor of each element. In other words, you can intialize each element through a copy constructor.
> 
> I suggest that we also provide a function equivalent where the function is provided a pointer to the memory to be initialized. This can be used for `NONCOPYABLE` classes, for example.
> 
> This is implemented using a SFINAE pattern because `nullptr` introduces ambiguity if you use static overload.
> 
> Currently running tier1-tier4.

> I think a more preferable approach is to do emplace-like filling
> 
> ```
> template <class... Args>
> E& at_grow(int i, Args... args) {
>     assert(0 <= i, "negative index %d", i);
>     if (i >= this->_len) {
>         if (i >= this->_capacity) {
>             grow(i);
>         }
>         for (int j = this->_len; j <= i; j++) {
>             _data[j].~E();
>             new (&_data[j]) E(args...);
>         }
>         this->_len = i + 1;
>     }
>     return _data[i];
> }
> ```

I think you might be right. If I understand this correctly we can pick between copy construction (having `Args` be equal to `E`) and "regular" construction depending on the arguments provided?

@stefank, @dean-long. Re: tests, yes, I should add tests. The goal here is to avoid copy construction, and I chose to provide a function so that you can yourself pick how to initialize the memory. I think @merykitty's solution might be preferable to mine.

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PR Comment: https://git.openjdk.org/jdk/pull/16409#issuecomment-1786888957