LabeledAxisAccessor.h

// Copyright 2023, UChicago Argonne, LLC
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// Software Name: NEML2 -- the New Engineering material Model Library, version 2
// By: Argonne National Laboratory
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#pragma once

#include <vector>
#include <iostream>

namespace neml2
{
/**
 * @brief The accessor containing all the information needed to access an item in a `LabeledAxis`.
 *
 * The accessor consists of an arbitrary number of item names. The last item name can be either a
 * variable name or a sub-axis name. All the other item names are considered to be sub-axis names.
 *
 * The LabeledAxisAccessor stores the item labels and does not resolve the actual layout of the
 * item. This way an accessor can be used access the same variable from different tensor layouts.
 *
 * The item names cannot contain whitespace, ".", ",", ";", or "/".
 */
class LabeledAxisAccessor
{
public:
  LabeledAxisAccessor() = default;

  template <typename... S>
  LabeledAxisAccessor(const char * name, S &&... names)
  {
    validate_item_name(name);
    _item_names.push_back(name);

    (validate_item_name(names), ...);
    (_item_names.push_back(names), ...);
  }

  template <typename... S>
  LabeledAxisAccessor(const std::string & name, S &&... names)
  {
    validate_item_name(name);
    _item_names.push_back(name);

    (validate_item_name(names), ...);
    (_item_names.push_back(names), ...);
  }

  LabeledAxisAccessor(const std::vector<std::string> & names);

  LabeledAxisAccessor(const LabeledAxisAccessor & other);

  /// Assignment operator
  LabeledAxisAccessor & operator=(const LabeledAxisAccessor & other);

  operator std::vector<std::string>() const;

  const std::vector<std::string> & vec() const { return _item_names; }

  bool empty() const;

  size_t size() const;

  /// Append a suffix to the item name.
  LabeledAxisAccessor with_suffix(const std::string & suffix) const;

  /// Add a new item
  LabeledAxisAccessor append(const LabeledAxisAccessor & axis) const;

  /// Re-mount the LabeledAxisAccessor on an axis by the axis accessor
  LabeledAxisAccessor on(const LabeledAxisAccessor & axis) const;

  /// Remove the leading \p n items from the labels.
  LabeledAxisAccessor slice(size_t n) const;

  /// Extract out the labels from \p n1 to \p n2
  LabeledAxisAccessor slice(size_t n1, size_t n2) const;

  /// Check if this accessor begins with another accessor
  bool start_with(const LabeledAxisAccessor & axis) const;

private:
  /// Throws if the item name has invalid format
  void validate_item_name(const std::string &) const;

  std::vector<std::string> _item_names;
};

/// Compare for equality between two LabeledAxisAccessor
bool operator==(const LabeledAxisAccessor & a, const LabeledAxisAccessor & b);

/// Compare for equality between two LabeledAxisAccessor
bool operator!=(const LabeledAxisAccessor & a, const LabeledAxisAccessor & b);

/**
 * @brief The (strict) smaller than operator is created so as to use LabeledAxisAccessor in sorted
 * data structures.
 */
bool operator<(const LabeledAxisAccessor & a, const LabeledAxisAccessor & b);

/**
 * @brief Serialize the \p accessor into a string. The format is simply the concatenation of all the
 * item names delimited by "/".
 */
std::ostream & operator<<(std::ostream & os, const LabeledAxisAccessor & accessor);
} // namespace neml2