//-----------------------------------------------------------------
//!
//! \brief value of first element
//!
//! Return the value of the first element in the linear view of
//! the array.
//!
//! \return value of the first element
//!
value_type front() const { return _data.front(); }
//-----------------------------------------------------------------
//!
//! \brief reference to first element
//!
//! Return a reference to the first element in the linear view of
//! the array.
//!
//! \return reference to first element
//!
value_type &front() { return _data.front(); }