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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CHROME_COMMON_STRING_ORDINAL_H_
#define CHROME_COMMON_STRING_ORDINAL_H_
#pragma once
#include <string>
// A StringOrdinal represents a specially-formatted string that can be used
// for ordering. The StringOrdinal class has an unbounded dense strict total
// order, which mean for any StringOrdinals a, b and c:
//
// - a < b and b < c implies a < c (transitivity);
// - exactly one of a < b, b < a and a = b holds (trichotomy);
// - if a < b, there is a StringOrdinal x such that a < x < b (density);
// - there are StringOrdinals x and y such that x < a < y (unboundedness).
//
// This means that when StringOrdinal is used for sorting a list, if
// any item changes its position in the list, only its StringOrdinal value
// has to change to represent the new order, and all the other older values
// can stay the same.
class StringOrdinal {
public:
// Creates a StringOrdinal from the given string. It may be valid or invalid.
explicit StringOrdinal(const std::string& string_ordinal);
// Creates an invalid StringOrdinal.
StringOrdinal();
// Creates a valid initial StringOrdinal, this is called to create the first
// element of StringOrdinal list (i.e. before we have any other values we can
// generate from).
static StringOrdinal CreateInitialOrdinal();
bool IsValid() const;
// All remaining functions can only be called if IsValid() holds.
// It is an error to call them if IsValid() is false.
// Order-related Functions
// Returns true iff |*this| < |other|.
bool LessThan(const StringOrdinal& other) const;
// Returns true iff |*this| > |other|.
bool GreaterThan(const StringOrdinal& other) const;
// Returns true iff |*this| == |other| (i.e. |*this| < |other| and
// |other| < |*this| are both false).
bool Equal(const StringOrdinal& other) const;
// Given |*this| != |other|, returns a StringOrdinal x such that
// min(|*this|, |other|) < x < max(|*this|, |other|). It is an error
// to call this function when |*this| == |other|.
StringOrdinal CreateBetween(const StringOrdinal& other) const;
// Returns a StringOrdinal |x| such that |x| < |*this|.
StringOrdinal CreateBefore() const;
// Returns a StringOrdinal |x| such that |*this| < |x|.
StringOrdinal CreateAfter() const;
// It is guaranteed that a StringOrdinal constructed from the returned
// string will be valid.
std::string ToString() const;
// Do this so we can use std::find on a std::vector of StringOrdinals.
bool operator==(const StringOrdinal& rhs) const;
// Use of copy constructor and default assignment for this class is allowed.
private:
// The string representation of the StringOrdinal.
std::string string_ordinal_;
// The validity of the StringOrdinal (i.e., is it of the format [a-z]*[b-z]),
// created to cache validity to prevent frequent recalculations.
bool is_valid_;
};
// A helper class that can be used by STL containers that require sorting.
class StringOrdinalLessThan {
public:
bool operator() (const StringOrdinal& lhs, const StringOrdinal& rhs) const;
};
#endif // CHROME_COMMON_STRING_ORDINAL_H_
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