Well this is an old topic but i've never seriously thought about it. We can grab a lot articles from internet, but here is what i agree most:
1. singleton is an instance, instance is an object. so, you can pass it as a parameter. If you were using static classes, the other function would have to use the class statically too and if you ever needed to change the behavior, you would need to rewrite parts of that function too instead of just having the first one pass a different class as the parameter.
2. You can also give a singleton some parameters. When working with static classes, you may need to pass a lot of parameters to the methods of the class because you aren't "constructing" it
3. singleton can become multiton(read db connection, write db connection)
4. If you use the reference in your class and decide that you won't need a singleton anymore, but a normal class, you will just need to change the behavior of the class itself and perhaps replace the line which gets an instance of it to constructing a new one or such. If you were using a static class, you would have to rewrite a lot of the code to use the new reference to the class instead of the static class name. A singleton class should also work almost out of the box as a normal class too. If you had a static class and wanted to convert it to a normal one, you would have to rewrite many parts of it.
6. You can't extend static classes, but singletons you can. Except it doesn't work very well in PHP due to some issues with static method inheritance, but it's not the only language in the world and it can be done but slightly hackily
7. Last and least:D dude, you can find many singleton in Zend Framework. Could you find any static class there?
So to the end, where is the place for static methods? Well, they definitely have their places too:
For example for library code they can be nice, such as the static System.Math class in C#
Showing posts with label static. Show all posts
Showing posts with label static. Show all posts
Wednesday, February 23, 2011
Wednesday, October 22, 2008
More about Singleton and static
Below is from 'http://my.opera.com/zomg/blog/2007/09/17/singleton-pattern-vs-static-classes'
Singleton also gives a reference/pointer to the class instance. You can then pass this reference as a parameter for some other function for example. If you were using static classes, the other function would have to use the class statically too and if you ever needed to change the behavior, you would need to rewrite parts of that function too instead of just having the first one pass a different class as the parameter.
There's also an another side to the reference thing. If you use the reference in your class and decide that you won't need a singleton anymore, but a normal class, you will just need to change the behavior of the class itself and perhaps replace the line which gets an instance of it to constructing a new one or such. If you were using a static class, you would have to rewrite a lot of the code to use the new reference to the class instead of the static class name. A singleton class should also work almost out of the box as a normal class too. If you had a static class and wanted to convert it to a normal one, you would have to rewrite many parts of it.
You can't extend static classes, but singletons you can. Except it doesn't work very well in PHP due to some issues with static method inheritance, but it's not the only language in the world and it can be done but slightly hackily.
So if we think about it with all this, why would you use static classes at all?
They have their uses too - For example for library code they can be nice, such as the static System.Math class in C#.
Singleton also gives a reference/pointer to the class instance. You can then pass this reference as a parameter for some other function for example. If you were using static classes, the other function would have to use the class statically too and if you ever needed to change the behavior, you would need to rewrite parts of that function too instead of just having the first one pass a different class as the parameter.
There's also an another side to the reference thing. If you use the reference in your class and decide that you won't need a singleton anymore, but a normal class, you will just need to change the behavior of the class itself and perhaps replace the line which gets an instance of it to constructing a new one or such. If you were using a static class, you would have to rewrite a lot of the code to use the new reference to the class instead of the static class name. A singleton class should also work almost out of the box as a normal class too. If you had a static class and wanted to convert it to a normal one, you would have to rewrite many parts of it.
You can't extend static classes, but singletons you can. Except it doesn't work very well in PHP due to some issues with static method inheritance, but it's not the only language in the world and it can be done but slightly hackily.
So if we think about it with all this, why would you use static classes at all?
They have their uses too - For example for library code they can be nice, such as the static System.Math class in C#.
Saturday, October 4, 2008
singleton, static, defensive programming
below quoted from PHP 5 CMS Framkwork Development.
"The singleton appears repeatedly, especially for the handler objects described later. In theory, handlers could be implemented as class methods, but in PHP5 a class is not itself a first class object and it is more effective to use singleton objects. Other objects are naturally singletons, such as the session object, since PHP5 handles only a single request at a time.
They(signleton classes) arise naturally in designing systems where a range of related services is needed. Sometimes, this is done by creating a class that consists only of static methods. But that is both inefficient, and inflexible. Dealing with an instance of a class is generally more efficient than dealing with static methods, and in many cases a singleton object will know quite a lot of potentially complex information. Since a class of this kind is a manager or handler, there should never be a need for more than a single instance of the class, hence the name singleton. "
Friday when i was looking into the codes of our system, i found piece of codes like below:
public function f($keyword, $country)
{
if ($keyword === 'a') {
$keyarray = $config[$country]['a'];
} elseif ($keyword == 'b') {
$keyarray = $config[$country]['b'];
}
foreach($keyarray as $key) {
......
}
}
What is the problem of the above code? First, $keyarray is not initialised! if $keyword is neither 'a' nor 'b', the program will still try to run the next codes and throw a notice: Undefined variable and a warning 'Warning: Invalid argument supplied for foreach()'.
In the above case, at lease we should put one more 'else{$keyarray = array()}' at the end to ensure $keyarray is initialised. It is better to check with isset to make sure $config is set up correctly. However, since many php programmers don't do this in practice.
My friend who was working in GE told me that none of PHP programmers are professionals, or all PHP programmers are amateur because PHP is designed for amateur to develop simple database driven website quickly. However, since PHP plays increasingly important role in web app development, enterprises tends to employ PHP developers for their web applications. As usual, they define the criteria like 3-5 years experiences, etc, etc. They never thought that PHP programmers with 3,5 years experiences means they don't have any formal, scientific software development methodology. Probably they know more detail of PHP language. They know more functions in PHP manual. But they don't have OOP in mind. They don't have design patterns in mind. They don't have refactoring in mind.
"The singleton appears repeatedly, especially for the handler objects described later. In theory, handlers could be implemented as class methods, but in PHP5 a class is not itself a first class object and it is more effective to use singleton objects. Other objects are naturally singletons, such as the session object, since PHP5 handles only a single request at a time.
They(signleton classes) arise naturally in designing systems where a range of related services is needed. Sometimes, this is done by creating a class that consists only of static methods. But that is both inefficient, and inflexible. Dealing with an instance of a class is generally more efficient than dealing with static methods, and in many cases a singleton object will know quite a lot of potentially complex information. Since a class of this kind is a manager or handler, there should never be a need for more than a single instance of the class, hence the name singleton. "
Friday when i was looking into the codes of our system, i found piece of codes like below:
public function f($keyword, $country)
{
if ($keyword === 'a') {
$keyarray = $config[$country]['a'];
} elseif ($keyword == 'b') {
$keyarray = $config[$country]['b'];
}
foreach($keyarray as $key) {
......
}
}
What is the problem of the above code? First, $keyarray is not initialised! if $keyword is neither 'a' nor 'b', the program will still try to run the next codes and throw a notice: Undefined variable and a warning 'Warning: Invalid argument supplied for foreach()'.
In the above case, at lease we should put one more 'else{$keyarray = array()}' at the end to ensure $keyarray is initialised. It is better to check with isset to make sure $config is set up correctly. However, since many php programmers don't do this in practice.
My friend who was working in GE told me that none of PHP programmers are professionals, or all PHP programmers are amateur because PHP is designed for amateur to develop simple database driven website quickly. However, since PHP plays increasingly important role in web app development, enterprises tends to employ PHP developers for their web applications. As usual, they define the criteria like 3-5 years experiences, etc, etc. They never thought that PHP programmers with 3,5 years experiences means they don't have any formal, scientific software development methodology. Probably they know more detail of PHP language. They know more functions in PHP manual. But they don't have OOP in mind. They don't have design patterns in mind. They don't have refactoring in mind.
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