IntroductionWhen PHP parser encounters an unqulified identifier such as class or function name, it resolves to current namespace. Therefore, to access PHP's predefined classes, they must be referred to by their fully qualified name by prefixing \.Using built-in classIn following example, a new class uses predefined stdClass as base class. We refer it by prefixing \ to specify global classExampleIncluded files will default to the global namespace. Hence, to refer to a class from included file, it must be prefixed with \Example#test1.php This file is included in another PHP script and its class is referred with \when this file is included ... Read More

IntroductionIn absence of any namespace definition, all definitions of class, function etc. are placed in a global namespace. If a name is prefixed with \ , it will mean that the name is required from the global space even in the context of the namespace.Using global space specificationExampleIncluded files will default to the global namespace.Example#test1.php this will print empty stringwhen this file is included in another namespaceExample#test2.php OutputThis will print following outputtestspace

IntroductionDeclaration of class, function and constants inside a namespace affects its acess, although any other PHP code can be present in it. PHP's namespace keyword is used to declare a new namespace. A file with .php extension must have namespace declaration in very first line after If namespace declaration is not at the top of file, PHP parser throws fatal errorExample Live Demo Hello world ?>OutputAbove code now returns name following errorPHP Fatal error: Namespace declaration statement has to be the very first statement or after any declare call in the scriptOnly declare construct can appear before namespace declarationExample

IntroductionIn PHP, namespace keyword is used to define a namespace. It is also used as an operator to request access to certain element in current namespace. The __NAMESPACE__ constant returns name of current namespace__NAMESPACE ConstantFrom a named namespace, __NAMESPACE__ returns its name, for global and un-named namespace it returns empty striingExample Live Demo#test1.php OutputAn empty string is returnedname of global namespace :For named namespace, its name is returnedExample Live DemoOutputname of current namespace : myspaceDynamic name construction__NAMESPACE__ is useful for constructing name dynamicallyExample Live Demo

IntroductionTraversing a big collection of data using looping construct such as foreach would require large memory and considerable processing time. With generators it is possible to iterate over a set of data without these overheads. A generator function is similar to a normal function. However, instead of return statement in a function, generator uses yield keyword to be executed repeatedly so that it provides values to be iterated.The yield keyword is the heart of generator mechanism. Even though its use appears to be similar to return, it doesn't stop execution of function. It provides next value for iteration and pauses ... Read More

IntroductionWhen a generator function is called, internally, a new object of Generator class is returned. It implements the Iterator interface. The iterator interface defines following abstract methodsIterator::current — Return the current elementIterator::key — Return the key of the current elementIterator::next — Move forward to next elementIterator::rewind — Rewind the Iterator to the first elementIterator::valid — Checks if current position is validGenerator acts as a forward-only iterator object would, and provides methods that can be called to manipulate the state of the generator, including sending values to and returning values from it.Generator as interatorIn following example, generator functions yields lines in a file ... Read More

IntroductionThrowable interface is implemented by Error and Exception class. All predefined Error classes are inherited from Error class. Instance of corresponding Error class is thrown inside try block and processed inside appropriate catch block.Throwing ErrorNormal execution (when no exception is thrown within the try block) will continue after that last catch block defined in sequence.Example Live DemoOutputFollowing output is displayed2 Caught exception: Division by zero. Execution continuesIn following example, TypeError is thrown while executing a function because appropriate arguments are not passed to it. Corresponding error message is displayedExample Live DemoOutputFollowing output is displayedArgument 2 passed to add() must be of the ... Read More

IntroductionBlocks of try - catch can be nested upto any desired levels. Exceptions will be handled in reverse order of appearance i.e. innermost exception processing is done first.ExampleIn following example,inner try block checks if either of two varibles are non-numeric, nd if so, throws a user defined exception. Outer try block throws DivisionByZeroError if denominator is 0. Otherwise division of two numbers is displayed.Example Live DemoOutputFollowing output is displayedDivision by 0 in line no 19Change any one of varibles to non-numeric valueerror : Non numeric data in line no 20If both variables are numbers, their division is printed

IntroductionPHP allows a series of catch blocks following a try block to handle different exception cases. Various catch blocks may be employed to handle predefined exceptions and errors as well as user defined exceptions.ExampleFollowing example uses catch blocks to process DivisioByZeroError, TypeError, ArgumentCountError and InvalidArgumentException conditions. There is also a catch block to handle general Exception.Example Live DemoOutputTo begin with, since denominator is 0, Divide by 0 error will be displayedDivision by 0Set $b=3 which will cause TypeError because divide function is expected to return integer but dividion results in floatReturn value of divide() must be of the type integer, float ... Read More

IntroductionPrior to version 7, PHP parser used to report errors in response to various conditions. Each error used to be of a certain predefined type. PHP7 has changed the mechanism of error reporting. Instead of traditional error reporting, most errors are now reported by throwing error exceptions.If error exceptions go unhandled, a fatal error is reported and will be handled like traditional error condition. PHP's error heirarchy starts from Throwable interface. All predefined errors such as ArithmeticError, AssertionError, CompileError and TypeError are classes implementing Throwable iterface. Exception in PHP 7 is also implements Throwable interface.Throwable interface acts as base for ... Read More