Introduce character_id type

src/avatar.cpp

@@ -605,7 +605,7 @@ bool avatar::read( int inventory_position, const bool continuous )
 
     add_msg( m_debug, "avatar::read: time_taken = %d", time_taken );
     player_activity act( activity_id( "ACT_READ" ), time_taken, continuous ? activity.index : 0,
-                         reader->getID() );
+                         reader->getID().get_value() );
     act.targets.emplace_back( item_location( *this, &it ) );
 
     // If the player hasn't read this book before, skim it to get an idea of what's in it.
@@ -660,11 +660,11 @@ bool avatar::read( int inventory_position, const bool continuous )
         } else if( skill && lvl < type->level ) {
             const double penalty = static_cast<double>( time_taken ) / time_to_read( it, *reader, elem );
             learners.insert( {elem, elem == reader ? _( " (reading aloud to you)" ) : ""} );
-            act.values.push_back( elem->getID() );
+            act.values.push_back( elem->getID().get_value() );
             act.str_values.push_back( to_string( penalty ) );
         } else {
             fun_learners.insert( {elem, elem == reader ? _( " (reading aloud to you)" ) : "" } );
-            act.values.push_back( elem->getID() );
+            act.values.push_back( elem->getID().get_value() );
             act.str_values.emplace_back( "1" );
         }
     }
@@ -709,7 +709,7 @@ bool avatar::read( int inventory_position, const bool continuous )
 
             if( skill ) {
                 const int lvl = get_skill_level( skill );
-                menu.addentry( getID(), lvl < type->level, '0',
+                menu.addentry( getID().get_value(), lvl < type->level, '0',
                                string_format( _( "Read until you gain a level | current level: %d" ), lvl ) );
             } else {
                 menu.addentry( -1, false, '0', _( "Read until you gain a level" ) );
@@ -719,7 +719,8 @@ bool avatar::read( int inventory_position, const bool continuous )
             if( skill && !learners.empty() ) {
                 add_header( _( "Read until this NPC gains a level:" ) );
                 for( const auto &elem : learners ) {
-                    menu.addentry( elem.first->getID(), true, -1, get_text( learners, elem ) );
+                    menu.addentry( elem.first->getID().get_value(), true, -1,
+                                   get_text( learners, elem ) );
                 }
             }
             if( !fun_learners.empty() ) {
@@ -754,7 +755,7 @@ bool avatar::read( int inventory_position, const bool continuous )
             menu.title = string_format( _( "Train %s from manual:" ),
                                         martial_art_learned_from( *it.type )->name );
             menu.addentry( -1, true, 1, _( "Train once." ) );
-            menu.addentry( getID(), true, 2, _( "Train until tired or success." ) );
+            menu.addentry( getID().get_value(), true, 2, _( "Train until tired or success." ) );
             menu.query( true );
             if( menu.ret == UILIST_CANCEL ) {
                 add_msg( m_info, _( "Never mind." ) );
@@ -779,10 +780,11 @@ bool avatar::read( int inventory_position, const bool continuous )
 
     if( !continuous ||
     !std::all_of( learners.begin(), learners.end(), [&]( const std::pair<npc *, std::string> &elem ) {
-    return std::count( activity.values.begin(), activity.values.end(), elem.first->getID() ) != 0;
+    return std::count( activity.values.begin(), activity.values.end(),
+                       elem.first->getID().get_value() ) != 0;
     } ) ||
     !std::all_of( activity.values.begin(), activity.values.end(), [&]( int elem ) {
-        return learners.find( g->find_npc( elem ) ) != learners.end();
+        return learners.find( g->find_npc( character_id( elem ) ) ) != learners.end();
     } ) ) {
 
         if( learners.size() == 1 ) {
@@ -943,7 +945,7 @@ void avatar::do_read( item &book )
 
     std::vector<std::pair<player *, double>> learners; //learners and their penalties
     for( size_t i = 0; i < activity.values.size(); i++ ) {
-        player *n = g->find_npc( activity.values[i] );
+        player *n = g->find_npc( character_id( activity.values[i] ) );
         if( n != nullptr ) {
             const std::string &s = activity.get_str_value( i, "1" );
             learners.push_back( { n, strtod( s.c_str(), nullptr ) } );
@@ -1015,7 +1017,7 @@ void avatar::do_read( item &book )
                 }
             } else {
                 //skill_level == originalSkillLevel
-                if( activity.index == learner->getID() ) {
+                if( activity.index == learner->getID().get_value() ) {
                     continuous = true;
                 }
                 if( learner->is_player() ) {
@@ -1077,7 +1079,7 @@ void avatar::do_read( item &book )
             m->second.call( *this, book, false, pos() );
             continuous = false;
         } else {
-            if( activity.index == g->u.getID() ) {
+            if( activity.index == g->u.getID().get_value() ) {
                 continuous = true;
                 switch( rng( 1, 5 ) ) {
                     case 1:

src/avatar.h

@@ -45,6 +45,9 @@ class avatar : public player
         void randomize( bool random_scenario, points_left &points, bool play_now = false );
         bool load_template( const std::string &template_name, points_left &points );
 
+        bool is_avatar() const override {
+            return true;
+        }
         avatar *as_avatar() override {
             return this;
         }

src/basecamp.cpp

@@ -447,7 +447,7 @@ void basecamp::validate_assignees()
             ++it2;
         }
     }
-    for( auto elem : g->get_follower_list() ) {
+    for( character_id elem : g->get_follower_list() ) {
         npc_ptr npc_to_add = overmap_buffer.find_npc( elem );
         if( !npc_to_add ) {
             continue;

src/cata_tiles.cpp

@@ -1692,7 +1692,7 @@ bool cata_tiles::draw_from_id_string( std::string id, TILE_CATEGORY category,
             // NPC
             if( id.substr( 4 ) == "npc_" ) {
                 if( npc *const guy = g->critter_at<npc>( pos ) ) {
-                    seed = guy->getID();
+                    seed = guy->getID().get_value();
                     break;
                 }
             }

src/character.cpp

@@ -123,7 +123,8 @@ Character::Character() :
     hp_cur( {{ 0 }} ),
     hp_max( {{ 0 }} ),
     damage_bandaged( {{ 0 }} ),
-    damage_disinfected( {{ 0 }} )
+    damage_disinfected( {{ 0 }} ),
+    id( -1 )
 {
     str_max = 0;
     dex_max = 0;
@@ -159,6 +160,22 @@ Character::~Character() = default;
 Character::Character( Character && ) = default;
 Character &Character::operator=( Character && ) = default;
 
+void Character::setID( character_id i )
+{
+    if( id.is_valid() ) {
+        debugmsg( "tried to set id of a npc/player, but has already a id: %d", id.get_value() );
+    } else if( !i.is_valid() ) {
+        debugmsg( "tried to set invalid id of a npc/player: %d", i.get_value() );
+    } else {
+        id = i;
+    }
+}
+
+character_id Character::getID() const
+{
+    return this->id;
+}
+
 field_type_id Character::bloodType() const
 {
     if( has_trait( trait_ACIDBLOOD ) ) {

src/character.h

@@ -18,6 +18,7 @@
 
 #include "bodypart.h"
 #include "calendar.h"
+#include "character_id.h"
 #include "creature.h"
 #include "game_constants.h"
 #include "inventory.h"
@@ -165,6 +166,10 @@ class Character : public Creature, public visitable<Character>
     public:
         ~Character() override;
 
+        character_id getID() const;
+        // sets the ID, will *only* succeed when the current id is not valid
+        void setID( character_id i );
+
         field_type_id bloodType() const override;
         field_type_id gibType() const override;
         bool is_warm() const override;
@@ -962,6 +967,9 @@ class Character : public Creature, public visitable<Character>
         mutable pimpl<pathfinding_settings> path_settings;
 
     private:
+        // A unique ID number, assigned by the game class. Values should never be reused.
+        character_id id;
+
         /** Needs (hunger, starvation, thirst, fatigue, etc.) */
         int stored_calories;
         int healthy_calories;

src/character_id.h

@@ -0,0 +1,58 @@
+#pragma once
+#ifndef CATA_CHARACTER_ID_H
+#define CATA_CHARACTER_ID_H
+
+#include <cassert>
+#include <ostream>
+
+class JsonIn;
+class JsonOut;
+
+class character_id
+{
+    public:
+        character_id() : value( -1 ) {}
+
+        explicit character_id( int i ) : value( i ) {
+        }
+
+        bool is_valid() const {
+            return value > 0;
+        }
+
+        int get_value() const {
+            return value;
+        }
+
+        character_id &operator++() {
+            ++value;
+            return *this;
+        }
+
+        void serialize( JsonOut & ) const;
+        void deserialize( JsonIn & );
+    private:
+        int value;
+};
+
+inline bool operator==( character_id l, character_id r )
+{
+    return l.get_value() == r.get_value();
+}
+
+inline bool operator!=( character_id l, character_id r )
+{
+    return l.get_value() != r.get_value();
+}
+
+inline bool operator<( character_id l, character_id r )
+{
+    return l.get_value() < r.get_value();
+}
+
+inline std::ostream &operator<<( std::ostream &o, character_id id )
+{
+    return o << id.get_value();
+}
+
+#endif // CATA_CHARACTER_ID_H

src/computer.cpp

@@ -1706,7 +1706,7 @@ SEARCHING FOR NEAREST REFUGEE CENTER, PLEASE WAIT ... " ) );
     } );
 
     if( !has_mission ) {
-        const auto mission = mission::reserve_new( mission_type, -1 );
+        const auto mission = mission::reserve_new( mission_type, character_id() );
         mission->assign( g->u );
         mission_target = mission->get_target();
     }

src/creature.h

@@ -78,6 +78,9 @@ class Creature
         virtual bool is_player() const {
             return false;
         }
+        virtual bool is_avatar() const {
+            return false;
+        }
         virtual bool is_npc() const {
             return false;
         }

src/game.cpp

@@ -545,7 +545,7 @@ void game::init_ui( const bool resized )
 
     // Only refresh if we are in-game, otherwise all resources are not initialized
     // and this refresh will crash the game.
-    if( resized && u.getID() != -1 ) {
+    if( resized && u.getID().is_valid() ) {
         refresh_all();
     }
 }
@@ -628,7 +628,7 @@ void game::setup()
 
     m = map( get_option<bool>( "ZLEVELS" ) );
 
-    next_npc_id = 1;
+    next_npc_id = character_id( 1 );
     next_mission_id = 1;
     new_game = true;
     uquit = QUIT_NO;   // We haven't quit the game
@@ -855,7 +855,7 @@ bool game::start_game()
     }
     // Assign all of this scenario's missions to the player.
     for( const mission_type_id &m : scen->missions() ) {
-        const auto mission = mission::reserve_new( m, -1 );
+        const auto mission = mission::reserve_new( m, character_id() );
         mission->assign( u );
     }
 
@@ -1838,7 +1838,7 @@ int game::assign_mission_id()
     return ret;
 }
 
-npc *game::find_npc( int id )
+npc *game::find_npc( character_id id )
 {
     return overmap_buffer.find_npc( id ).get();
 }
@@ -1882,13 +1882,13 @@ void game::record_npc_kill( const npc &p )
     npc_kills.push_back( p.get_name() );
 }
 
-void game::add_npc_follower( const int &id )
+void game::add_npc_follower( const character_id &id )
 {
     follower_ids.insert( id );
     u.follower_ids.insert( id );
 }
 
-void game::remove_npc_follower( const int &id )
+void game::remove_npc_follower( const character_id &id )
 {
     follower_ids.erase( id );
     u.follower_ids.erase( id );
@@ -1940,7 +1940,7 @@ void game::validate_camps()
     }
 }
 
-std::set<int> game::get_follower_list()
+std::set<character_id> game::get_follower_list()
 {
     return follower_ids;
 }
@@ -2715,7 +2715,7 @@ void game::load( const save_t &name )
         e->set_owner( g->faction_manager_ptr->get( faction_id( "your_followers" ) ) );
     }
     // legacy, needs to be here as we access the map.
-    if( u.getID() == 0 || u.getID() == -1 ) {
+    if( !u.getID().is_valid() ) {
         // player does not have a real id, so assign a new one,
         u.setID( assign_npc_id() );
         // The vehicle stores the IDs of the boarded players, so update it, too.
@@ -3755,10 +3755,10 @@ void game::reset_light_level()
 }
 
 //Gets the next free ID, also used for player ID's.
-int game::assign_npc_id()
+character_id game::assign_npc_id()
 {
-    int ret = next_npc_id;
-    next_npc_id++;
+    character_id ret = next_npc_id;
+    ++next_npc_id;
     return ret;
 }
 
@@ -4681,7 +4681,7 @@ template std::shared_ptr<monster> game::shared_from<monster>( const monster & );
 template std::shared_ptr<npc> game::shared_from<npc>( const npc & );
 
 template<typename T>
-T *game::critter_by_id( const int id )
+T *game::critter_by_id( const character_id id )
 {
     if( id == u.getID() ) {
         // player is always alive, therefore no is-dead check
@@ -4691,9 +4691,9 @@ T *game::critter_by_id( const int id )
 }
 
 // monsters don't have ids
-template player *game::critter_by_id<player>( int );
-template npc *game::critter_by_id<npc>( int );
-template Creature *game::critter_by_id<Creature>( int );
+template player *game::critter_by_id<player>( character_id );
+template npc *game::critter_by_id<npc>( character_id );
+template Creature *game::critter_by_id<Creature>( character_id );
 
 monster *game::summon_mon( const mtype_id &id, const tripoint &p )
 {