[jira] [Created] (ARROW-8367) [C++] Is FromString(..., pool) worthwhile

["Ben Kietzman (Jira)" <ji...@apache.org>]

Ben Kietzman created ARROW-8367:
-----------------------------------

             Summary: [C++] Is FromString(..., pool) worthwhile
                 Key: ARROW-8367
                 URL: https://issues.apache.org/jira/browse/ARROW-8367
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
    Affects Versions: 0.16.0
            Reporter: Ben Kietzman
             Fix For: 1.0.0


From [https://github.com/apache/arrow/pull/6863#discussion_r404913683]

There are currently two overloads of {{Buffer::FromString}}, one which takes an rvalue reference to string and another which takes a const reference and a MemoryPool. In the former case the string is simply moved into a Buffer subclass while in the latter the MemoryPool is used to allocate space into which the string's contents are copied, which necessitates bubbling the potential allocation failure. This seems gratuitous given we don't use {{std::string}} to store large quantities so it should be fine to provide only
{code:java}
  static std::unique_ptr<Buffer> FromString(std::string data); 
{code}
and rely on {{std::string}}'s copy constructor when the argument is not an rvalue.

In the case of a {{std::string}} which may/does contain large data and must be copied, tracking the copied memory with a MemoryPool does not require a great deal of boilerplate:
{code:java}
ARROW_ASSIGN_OR_RAISE(auto buffer,
                      Buffer(large).CopySlice(0, large.size(), pool));
{code}



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