blob: 9573b07e84310b32638f010c05b355ea19ee8ead (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
|
// SPDX-License-Identifier: GPL-2.0
/*
* We use singletons in numerous places. In combination with QML this gives
* us a very fundamental problem, because QML likes to allocate objects by
* itself. There are known workarounds, but currently we use idiosyncratic
* singleton classes, which initialize the global instance pointer in the
* constructor. Things get even more complicated if the same singleton is used
* on mobile and on desktop. The latter might want to simply use the classical
* instance() function without having to initialize the singleton first, as
* that would beat the purpose of the instance() method.
*
* The template defined here, SillySingleton, codifies all this. Simply derive
* a class from this template:
* class X : public SillySingleton<X> {
* ...
* };
* This will generate an instance() method. This will do the right thing for
* both methods: explicit construction of the singleton via new or implicit
* by calling the instance() method. It will also generate warnings if a
* singleton class is generated more than once (i.e. first instance() is called
* and _then_ new).
*
* In the long run we should get rid of all users of this class.
*/
#ifndef SINGLETON_H
#define SINGLETON_H
#include <typeinfo>
#include <QtGlobal>
// 1) Declaration
template<typename T>
class SillySingleton {
static T *self;
protected:
SillySingleton();
~SillySingleton();
public:
static T *instance();
};
template<typename T>
T *SillySingleton<T>::self = nullptr;
// 2) Implementation
template<typename T>
SillySingleton<T>::SillySingleton()
{
if (self)
qWarning("Generating second instance of singleton %s", typeid(T).name());
self = static_cast<T *>(this);
qDebug("Generated singleton %s", typeid(T).name());
}
template<typename T>
SillySingleton<T>::~SillySingleton()
{
if (self == this)
self = nullptr;
else
qWarning("Destroying unknown instance of singleton %s", typeid(T).name());
qDebug("Destroyed singleton %s", typeid(T).name());
}
template<typename T>
T *SillySingleton<T>::instance()
{
if (!self)
new T;
return self;
}
#endif
|
