view base/ById.h @ 1833:21c792334c2e sensible-delimited-data-strings

Rewrite all the DelimitedDataString stuff so as to return vectors of individual cell strings rather than having the classes add the delimiters themselves. Rename accordingly to names based on StringExport. Take advantage of this in the CSV writer code so as to properly quote cells that contain delimiter characters.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#ifndef SV_BY_ID_H
#define SV_BY_ID_H

#include "Debug.h"

#include <memory>
#include <iostream>
#include <climits>
#include <stdexcept>

#include <QMutex>
#include <QString>

#include "XmlExportable.h"

/*
 * ById - central pool of objects to be retrieved by persistent id.
 *
 * This is a pretty simple mechanism for obtaining safe "borrowed"
 * references to shared objects, including across threads, based on an
 * object ID.
 *
 * A class (call it C) inherits WithTypedId<C>. This produces a type
 * C::Id containing a numerical id. Each instance of C (or subclass
 * thereof) has an internal id of type C::Id whose value is unique
 * among all ids ever possessed by any instances of all classes that
 * use this id mechanism (within a single run of the program).
 *
 * Then we have a static store of type TypedById<C, C::Id>. This holds
 * a set of heap-allocated C objects (or subclass thereof) and hands
 * out shared_ptr references to them when queried by id. The
 * application calls add() to pass an object to the store (which takes
 * ownership of it), and the application calls release() when it
 * thinks it has finished with an object, to request the store to
 * delete it.
 *
 * Note that an object's id can't (without shenanigans) be queried
 * directly from that object - it is returned when the object is added
 * to a ById store. So if you have an object id, you know that the
 * object must have been added to a store at some point.
 *
 * The goal is to improve code that would previously have retained a
 * bare pointer to a heap-allocated object that it did not own. For
 * example, in Sonic Visualiser we have a Model hierarchy of complex
 * mutable objects, and any given model may be referred to by many
 * different layers, transforms (as both source and target) etc. Using
 * bare pointers for those references means that we need everything to
 * be notified (and act properly on the notification) if a model is
 * about to be deleted. Using a Model::Id instead gives the code a
 * guarantee: if the model has been deleted since you last looked at
 * it, then the ById store will return a null shared_ptr from its
 * get() function for that id; but if it returns a non-null
 * shared_ptr, then the object being pointed to can't be deleted while
 * that shared_ptr is in scope.
 *
 * Example:
 *
 * class Thing : public WithTypedId<Thing> { Thing(int x) { } };
 * typedef TypedById<Thing, Thing::Id> ThingById;
 *
 * // application creates a new Thing
 * // ...
 * auto thing = std::make_shared<Thing>(10);
 * auto thingId = ThingById::add(thing);
 *
 * // application then passes thingId to something else, without
 * // storing the shared_ptr anywhere - the ById store manages that
 * 
 * // code elsewhere now has the thingId, and needs to use the Thing
 * // ...
 * void doSomething() {
 *     auto thing = ThingById::get(m_thingId);
 *     if (!thing) { // the Thing has been deleted, stop acting on it
 *         return;   // (this may be an error or it may be unexceptional)
 *     }
 *     // now we have a guarantee that the thing ptr will be valid
 *     // until it goes out of scope when doSomething returns
 * }
 *
 * // application wants to be rid of the Thing
 * ThingById::release(thingId);
 */

//!!! to do: review how often we are calling getAs<...> when we could
// just be using get

struct IdAlloc {

    // The value NO_ID (-1) is never allocated
    static const int NO_ID = -1;
    
    static int getNextId();
};

template <typename T>
struct TypedId {
    
    int untyped;
    
    TypedId() : untyped(IdAlloc::NO_ID) {}

    TypedId(const TypedId &) =default;
    TypedId &operator=(const TypedId &) =default;

    bool operator==(const TypedId &other) const {
        return untyped == other.untyped;
    }
    bool operator!=(const TypedId &other) const {
        return untyped != other.untyped;
    }
    bool operator<(const TypedId &other) const {
        return untyped < other.untyped;
    }
    bool isNone() const {
        return untyped == IdAlloc::NO_ID;
    }
};

template <typename T>
std::ostream &
operator<<(std::ostream &ostr, const TypedId<T> &id)
{
    // For diagnostic purposes only. Do not use these IDs for
    // serialisation - see XmlExportable instead.
    if (id.isNone()) {
        return (ostr << "<none>");
    } else {
        return (ostr << "#" << id.untyped);
    }
}

class WithId
{
public:
    WithId() :
        m_id(IdAlloc::getNextId()) {
    }
    virtual ~WithId() {
    }

protected:
    friend class AnyById;
    
    /**
     * Return an id for this object. The id is a unique number for
     * this object among all objects that implement WithId within this
     * single run of the application.
     */
    int getUntypedId() const {
        return m_id;
    }

private:
    int m_id;
};

template <typename T>
class WithTypedId : virtual public WithId
{
public:
    typedef TypedId<T> Id;
    
    WithTypedId() : WithId() { }

protected:
    template <typename Item, typename Id>
    friend class TypedById;
    
    /**
     * Return an id for this object. The id is a unique value for this
     * object among all objects that implement WithTypedId within this
     * single run of the application.
     */
    Id getId() const {
        Id id;
        id.untyped = getUntypedId();
        return id;
    }
};

class AnyById
{
public:
    static int add(std::shared_ptr<WithId>);
    static void release(int);
    static std::shared_ptr<WithId> get(int); 

    template <typename Derived>
    static bool isa(int id) {
        std::shared_ptr<WithId> p = get(id);
        return bool(std::dynamic_pointer_cast<Derived>(p));
    }
   
    template <typename Derived>
    static std::shared_ptr<Derived> getAs(int id) {
        std::shared_ptr<WithId> p = get(id);
        return std::dynamic_pointer_cast<Derived>(p);
    }

private:
    class Impl;
    static Impl &impl();
};

template <typename Item, typename Id>
class TypedById
{
public:
    static Id add(std::shared_ptr<Item> item) {
        Id id;
        id.untyped = AnyById::add(item);
        return id;
    }

    static void release(Id id) {
        AnyById::release(id.untyped);
    }
    static void release(std::shared_ptr<Item> item) {
        release(item->getId());
    }

    template <typename Derived>
    static bool isa(Id id) {
        return AnyById::isa<Derived>(id.untyped);
    }

    template <typename Derived>
    static std::shared_ptr<Derived> getAs(Id id) {
        return AnyById::getAs<Derived>(id.untyped);
    }

    static std::shared_ptr<Item> get(Id id) {
        return getAs<Item>(id);
    }
    
    /**
     * If the Item type is an XmlExportable, return the export ID of
     * the given item ID. A call to this function will fail to compile
     * if the Item is not an XmlExportable.
     *
     * The export ID is a simple int, and is only allocated when first
     * requested, so objects that are never exported don't get one.
     */
    static int getExportId(Id id) {
        auto exportable = getAs<XmlExportable>(id);
        if (exportable) {
            return exportable->getExportId();
        } else {
            return XmlExportable::NO_ID;
        }
    }
};

#endif