Notes on php

The limitations of cookies :-

1) the cokkie specification says that 

I) no cookie can exceed 4KB in size,

II) only 20 cookies are allowed per domain ,

III) and a total of 300 cookies can be stored on the client side

2) There is no control over when the browsers actually expire cookies.

Type juggling :-

1) The conversion of a value from one type to another is called casting.

2) This kind of implicit casting is called type juggling in PHP.

Regular expressions:-

1) Definition :- A regular expression is a string that represents a pattern .The regular expression functions compare that pattern to another string and see if any of the string matches the pattern .Some functions tell you whether there was a match, while others make changes to the string.

2) PHP provides support for two different types of regular expressions :

1) POSIX and 

2) Perl- compatible

3) POSIX regular expressions are less powerful and sometimes slower , than the Perl - compatible functions ,but can be easier to read.

4)There are three uses for regular expressions:

1) matching ,which can also be used to extract information from a string ;

2) substituting new text for matching text; and

3) spilitting a string into an array of smaller chunks.

5) PHP has functions for all three behaviours for both Perl and POSIX regular expressions .For instance ,erg() does a POSIX match ,while preg_match() does a Perl match .

6) Fortunately ,there are a number of similarities between basic POIX and Perl regular expressions, so we'll cover those before dealing into the details of each library. 

Serialzation:-

1) Serializing an object means converting it to bytestream representation that can be stored in a file. This  is useful for persistent data , for example , PHP sessions automatically save and restore object.

2) Serialization in PHP is mostly automatic - it requires little extra work from you.

Design pattern

Why design pattern?
To make project new libraries are created.
New classes can be used for further program i.e. Classes are reusable.
Thus the problem which is reusable is design pattern.


Definition Design Pattern
Each pattern describes a problem which occurs over and over again in our environment and then describes the code of the solution to that problem in such a way that you can use this solution a million times over without ever doing it the same way twice.

Elements of design pattern :-
1) Pattern name
2) Problem
3) Solution
4) Consequences

The person requires documentation for design pattern i.e. Describing design pattern.
For this there are as follows:-
1) Pattern name and classification
2) Intent
3) Also known as ( different names for them e.g. Abstract class has user class name )
4) Motivation ( why person problem to motivate for design pattern )
5) Applicability ( Real life situations where used )
6) Structure ( data structures )
7) Participants ( objects and components )
8 ) Collaboration (collaborate)
9) Consequences ( Advantage and disadvantages) also drawbacks
10) Implementation
11) Sample code( code of any object oriented language )
12) Known Uses
13) Related Patterns .( relationship with other design pattern)
14) Factory methods ( only methods used for design pattern)

The catalog of design pattern :-
1) Abstract factory
2) Prototype
3) Singleton ( means single object )
4) Adaptor
5) Decorator
6) Proxy
7) Command
8) Observer
9) Strategy

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