Class IO

include/process/subprocess.hpp:61–145

   *   3. FD: Redirect to an open file descriptor.
   */
  class IO
  {
  public:
    /**
     * For input file descriptors a child reads from the `read` file
     * descriptor and a parent may write to the `write` file
     * descriptor if one is present.
     *
     * NOTE: We initialize `read` to -1 so that we do not close an
     * arbitrary file descriptor, in case we encounter an error
     * while starting a subprocess (closing -1 is always a no-op).
     */
    struct InputFileDescriptors
    {
      int_fd read = -1;
      Option<int_fd> write = None();
    };

    /**
     * For output file descriptors a child writes to the `write` file
     * descriptor and a parent may read from the `read` file
     * descriptor if one is present.
     *
     * NOTE: We initialize `write` to -1 so that we do not close an
     * arbitrary file descriptor, in case we encounter an error
     * while starting a subprocess (closing -1 is always a no-op).
     */
    struct OutputFileDescriptors
    {
      Option<int_fd> read = None();
      int_fd write = -1;
    };

    /**
     * Describes the lifecycle of a file descriptor passed into a subprocess
     * via the `Subprocess::FD` helper.
     */
    enum FDType {
      /**
       * The file descriptor is duplicated before being passed to the
       * subprocess.  The original file descriptor remains open.
       */
      DUPLICATED,

      /**
       * The file descriptor is not duplicated before being passed to the
       * subprocess.  Upon spawning the subprocess, the original file
       * descriptor is closed in the parent and remains open in the child.
       */
      OWNED
    };


  private:
    friend class Subprocess;

    friend Try<Subprocess> subprocess(
        const std::string& path,