[PATCH] Exploit move semantics in std::accumulate.

[Eelis van der Weegen]

The attached simple patch reduces the runtime of the following program
from 1.4 seconds to 0.005 seconds on my machine:

  #include <iostream>
  #include <string>
  #include <numeric>
  #include <vector>

  int main()
  {
    std::vector<std::string> v;
    for(int i = 0; i != 20000; ++i)
      v.push_back(std::string(50, 'a'+(i%10)));

    std::cout << std::accumulate(v.begin(), v.end(),
      std::string()).size() << '\n';
  }

Regards,

Eelis
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