Game entity manager (C++)

EntityManager.cpp

/**
    EntityManager.cpp
    Implements the EntityManager class, representing
    a collection of Entities responsible for their
    instantiation.

    @author Sam Griffiths
    www.computist.xyz
*/

#include "EntityManager.h"

#include <algorithm>

EntityID EntityManager::instantiate(std::string name)
{
    //Add to collection and log in lookup
    std::shared_ptr<Entity> e = std::make_shared<Entity>(name);
    entityLookup.insert({ e->id(), entities.size() });
    entities.push_back(e);
    return e->id();
}

std::weak_ptr<Entity> EntityManager::get(EntityID id)
{
    auto it = entityLookup.find(id);
    if (it != entityLookup.end())
        return std::weak_ptr<Entity>(entities[it->second]);
    else
        return std::weak_ptr<Entity>();
}

void EntityManager::remove(EntityID id)
{
    auto it = entityLookup.find(id);
    if (it != entityLookup.end())
    {
        EntityCollectionIndex i = it->second;
        EntityID back = entities.back()->id();

        //Swap and pop
        std::swap(entities[i], entities.back());
        entities.pop_back();

        entityLookup[back] = i;
        entityLookup.erase(id);
    }
}

EntityManager.h

/**
    EntityManager.h
    Declares the EntityManager class, representing
    a collection of Entities responsible for their
    instantiation.

    @author Sam Griffiths
    www.computist.xyz
*/

#pragma once

#include <memory>
#include <vector>
#include <unordered_map>

#include "Entity.h"

typedef std::vector<std::shared_ptr<Entity>> EntityCollection;
typedef EntityCollection::size_type EntityCollectionIndex;

class EntityManager
{
private:
    EntityCollection entities;
    std::unordered_map<EntityID, EntityCollectionIndex> entityLookup;

public:
    //Creates a new Entity, returning its allocated ID
    EntityID instantiate(std::string name);

    //Gets a pointer to the Entity of the given ID
    std::weak_ptr<Entity> get(EntityID id);

    //Deletes the Entity of the given ID
    void remove(EntityID id);
};