php variable assignment in function

• Variable Function

PHP variable function is a variable that is used to assign a function name with parentheses “()”. However, the PHP interpreter checks if it contains a callback or a function which should exist in the PHP project. If it doesn’t exist, the interpreter will produce an error.

Let’s see how to do that.

How to Assign a Function to Variable using PHP

According to this concept, PHP allow us to write a string inside a variable which can be called later as a function callback. Here is an example.

In this example, I assigned a string value to the variable “$func”, which contains the function name “codedtag”. Then, I defined the function with the same name as this string.

In the following line, I called the variable as a function “$func()”. However, when the interpreter reads it, it will connect the parentheses “()” with the string inside the variable and consider it as a callback.

Additionally, the PHP interpreter will consider this as a variable function, so if the function is not found during execution, the interpreter will stop executing the code immediately and show you an error message.

Here’s an example to demonstrate this scenario.

In this example, I called an undefined function, which is “calling_func”. That means PHP has to execute this function, “calling_func()”. But it is not defined yet in the document. So, it will show you the following error.

Anyway, let’s focus on another aspect of PHP variable functions, which involves the functions inside a class.

Assign a PHP Function of Class as a Variable

In PHP, you can also use the methods of a class as variables with parentheses to call them once an instance of the class is created.

Here is an example:

In this example, we can see that the “$group” variable stores the name of the method, which can be called by using parentheses.

But, what if the method inside the class contains a static property? Let’s see how it works with the example below.

One way to call the function using the variable name as a function name is by using the scope resolution operator like this: $obj::$group() .

Moreover, there is another method that works on PHP 5.4 and above. It allows us to use a complex callback. For example:

Let’s see how it works with the static method.

In both of these examples, the array acts as a function by implementing the class object, with the function being callable once it finds that the main variable has parentheses.

You learned how to assign a function to a PHP variable, but how to pass arguments within? Let’s focus on this in the following section.

Variable Function and Arguments

You can follow the same approach and pass the arguments into the parentheses of the variable function.

In the above example, the $func variable contains the string name “count”. When invoked with parentheses, PHP looks for the count() function, which requires a countable element as an argument.

However, some PHP predefined callbacks, such as language constructs (e.g., require, empty, include, isset, print, unset, and echo), will not work with variables.

This will show you a fetal error in PHP like the below.

Anyway, Let’s summarize it.

Wrapping Up

During this tutorial, you learned what variable functions are and how to use them with a class, static methods, and more. Here is the explanation in a few points:

• The variable functions in PHP lets you use a variable as a function name. You assign the name of a function to a variable. And then, you call it with parentheses.
• Assign "codedtag" to a variable $func . Define a function codedtag() . Call $func() to execute codedtag() .
• If the assigned function doesn’t exist, PHP stops. It shows a fatal error. This means the function is undefined.
• You can assign methods from a class to variables. Call these methods through the variable. Use the scope resolution operator ( :: ) for static methods.
• Variable functions can take arguments. Include them within the calling parentheses.
• Some PHP constructs like require and empty can’t be variable functions. Trying this results in a fatal error.

Thank you for reading. Happy Coding!

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PHP Variable functions

Introduction.

If name of a variable has parentheses (with or without parameters in it) in front of it, PHP parser tries to find a function whose name corresponds to value of the variable and executes it. Such a function is called variable function. This feature is useful in implementing callbacks, function tables etc.

Variable functions can not be built eith language constructs such as include, require, echo etc. One can find a workaround though, using function wrappers.

Variable function example

In following example, value of a variable matches with function of name. The function is thus called by putting parentheses in front of variable

 Live Demo

This will produce following result. −

Here is another example of variable function with arguments

In following example, name of function to called is input by user

Variable method example

Concept of variable function can be extended to method in a class

A static method can be also called by variable method technique

This will now throw exception as follows −

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Home » PHP Tutorial » PHP Assignment Operators

PHP Assignment Operators

Summary : in this tutorial, you will learn about the most commonly used PHP assignment operators.

Introduction to the PHP assignment operator

PHP uses the = to represent the assignment operator. The following shows the syntax of the assignment operator:

On the left side of the assignment operator ( = ) is a variable to which you want to assign a value. And on the right side of the assignment operator ( = ) is a value or an expression.

When evaluating the assignment operator ( = ), PHP evaluates the expression on the right side first and assigns the result to the variable on the left side. For example:

In this example, we assigned 10 to $x, 20 to $y, and the sum of $x and $y to $total.

The assignment expression returns a value assigned, which is the result of the expression in this case:

It means that you can use multiple assignment operators in a single statement like this:

In this case, PHP evaluates the right-most expression first:

The variable $y is 20 .

The assignment expression $y = 20 returns 20 so PHP assigns 20 to $x . After the assignments, both $x and $y equal 20.

Arithmetic assignment operators

Sometimes, you want to increase a variable by a specific value. For example:

How it works.

• First, $counter is set to 1 .
• Then, increase the $counter by 1 and assign the result to the $counter .

After the assignments, the value of $counter is 2 .

PHP provides the arithmetic assignment operator += that can do the same but with a shorter code. For example:

The expression $counter += 1 is equivalent to the expression $counter = $counter + 1 .

Besides the += operator, PHP provides other arithmetic assignment operators. The following table illustrates all the arithmetic assignment operators:

Concatenation assignment operator

PHP uses the concatenation operator (.) to concatenate two strings. For example:

By using the concatenation assignment operator you can concatenate two strings and assigns the result string to a variable. For example:

• Use PHP assignment operator ( = ) to assign a value to a variable. The assignment expression returns the value assigned.
• Use arithmetic assignment operators to carry arithmetic operations and assign at the same time.
• Use concatenation assignment operator ( .= )to concatenate strings and assign the result to a variable in a single statement.

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Variables are "containers" for storing information.

Creating (Declaring) PHP Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable:

In the example above, the variable $x will hold the value 5 , and the variable $y will hold the value "John" .

Note: When you assign a text value to a variable, put quotes around the value.

Note: Unlike other programming languages, PHP has no command for declaring a variable. It is created the moment you first assign a value to it.

Think of variables as containers for storing data.

A variable can have a short name (like $x and $y ) or a more descriptive name ( $age , $carname , $total_volume ).

Rules for PHP variables:

• A variable starts with the $ sign, followed by the name of the variable
• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case-sensitive ( $age and $AGE are two different variables)

Remember that PHP variable names are case-sensitive!

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Output Variables

The PHP echo statement is often used to output data to the screen.

The following example will show how to output text and a variable:

The following example will produce the same output as the example above:

The following example will output the sum of two variables:

Note: You will learn more about the echo statement and how to output data to the screen in the PHP Echo/Print chapter .

PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.

In PHP 7, type declarations were added. This gives an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.

You will learn more about strict and non-strict requirements, and data type declarations in the PHP Functions chapter.

Variable Types

PHP has no command for declaring a variable, and the data type depends on the value of the variable.

PHP supports the following data types:

• Float (floating point numbers - also called double)

Get the Type

To get the data type of a variable, use the var_dump() function.

The var_dump() function returns the data type and the value:

See what var_dump() returns for other data types:

Assign String to a Variable

Assigning a string to a variable is done with the variable name followed by an equal sign and the string:

String variables can be declared either by using double or single quotes, but you should be aware of the differences. Learn more about the differences in the PHP Strings chapter .

Assign Multiple Values

You can assign the same value to multiple variables in one line:

All three variables get the value "Fruit":

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PHP Variable Explained: Learn How to Use It

After you learn PHP basics, you will see dollar signs not only in your dreams but also on your screen, as this symbol ($) is used to mark variables. A PHP variable is similar to a little container that is used to store information (value). A value usually consists of letters or numbers, but a variable can also exist without storing any value.

You are not required to declare a variable before adding a value to it. The first time you assign a value to a particular variable name, you create a variable. The value is assigned by using the equal sign, also called the assignment operator (=). Repetition of the process with the same name results in a change of value.

PHP will also automatically understand the type of the variable according to the value you have assigned to it. The context in which a particular PHP variable works is called PHP variable scope.

• 1. PHP Variable: Main Tips
• 2. What a Variable Is
• 3. Way to Output
• 4. The Scope
• 5. PHP Variable: Summary

PHP Variable: Main Tips

• PHP variables start with a $ sign.
• PHP variables are used to store information (value).
• The name of a variable can begin with a letter or an underscore character (_), but never a number. However, it may contain numbers.
• Variables are case-sensitive .

What a Variable Is

A PHP variable may have a name as long or short as you wish. It can consist of one letter (x, y, z, and so on) or a whole bunch of them (tree, household, thelongestwordinthewholewideworld).

The example below shows that the variable $text is a container to the value of Hey coders! and both $x and $y variables hold their respective values of 9 and 1.

Note: In order to assign text to a variable correctly, quotes are used. They are not needed for numerical values.

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Way to Output

If you wish to output the information to the screen, it's easy to do by using an echo statement. In the example below, you can see a PHP variable being used in the echo statement. The result will be the output of both statement text and the value that has been assigned to the $website variable.

The user can declare variables anywhere in the PHP script, outside of a function or within one. The exact part in which a certain variable can be used is called PHP variable scope . There are three main scopes:

Local vs. Global

By expressing a PHP variable outside the function, you make it a PHP Global variable. This means that a certain variable can be used anywhere outside the function.

If you express a variable inside the function, it gives it a Local variable scope. As the name suggests, this PHP variable will be only usable locally: inside that particular function.

Note: Different variables with local PHP variable scopes can have identical names and still be executed correctly if they are used within different functions.

If you wish to use a PHP global variable inside a certain function, you should use the keyword global in front of the variable. In the example below you can see how PHP variables $x and $y are used inside a function called learnTest() .

Global variables are stored in a $GLOBALS[index] array. These variables can be accessed and updated without leaving the function. This example illustrates how it works in the learnTest() function:

A local PHP variable scope also indicates that after a certain function is done, the variables inside are deleted. Sometimes, we might prefer to keep them longer.

For a local variable to stay after the function is executed, a static keyword must be used when declaring it. You can see an example of how it is applied on the PHP variable $x below.

The variable will keep both its local scope and the data it held before. It will not be deleted, no matter how many times you will repeat the function.

PHP Variable: Summary

• You can recognize a PHP variable from a first glance, as it always starts with a $ . While it's name can contain numbers, it cannot start with one: the first symbol must be either a letter or an underscore (_).
• Information stored in a certain PHP variable is called value.
• Unlike functions, variables are case-sensitive .

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• Language Reference

Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive.

Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: ^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$

Note : For our purposes here, a letter is a-z, A-Z, and the bytes from 128 through 255 ( 0x80-0xff ).

Note : $this is a special variable that can't be assigned. Prior to PHP 7.1.0, indirect assignment (e.g. by using variable variables ) was possible.

See also the Userland Naming Guide .

For information on variable related functions, see the Variable Functions Reference .

<?php $var = 'Bob' ; $Var = 'Joe' ; echo " $var , $Var " ; // outputs "Bob, Joe" $ 4site = 'not yet' ; // invalid; starts with a number $_4site = 'not yet' ; // valid; starts with an underscore $täyte = 'mansikka' ; // valid; 'ä' is (Extended) ASCII 228. ?>

By default, variables are always assigned by value. That is to say, when you assign an expression to a variable, the entire value of the original expression is copied into the destination variable. This means, for instance, that after assigning one variable's value to another, changing one of those variables will have no effect on the other. For more information on this kind of assignment, see the chapter on Expressions .

PHP also offers another way to assign values to variables: assign by reference . This means that the new variable simply references (in other words, "becomes an alias for" or "points to") the original variable. Changes to the new variable affect the original, and vice versa.

To assign by reference, simply prepend an ampersand (&) to the beginning of the variable which is being assigned (the source variable). For instance, the following code snippet outputs ' My name is Bob ' twice: <?php $foo = 'Bob' ; // Assign the value 'Bob' to $foo $bar = & $foo ; // Reference $foo via $bar. $bar = "My name is $bar " ; // Alter $bar... echo $bar ; echo $foo ; // $foo is altered too. ?>

One important thing to note is that only named variables may be assigned by reference. <?php $foo = 25 ; $bar = & $foo ; // This is a valid assignment. $bar = &( 24 * 7 ); // Invalid; references an unnamed expression. function test () { return 25 ; } $bar = & test (); // Invalid. ?>

It is not necessary to initialize variables in PHP however it is a very good practice. Uninitialized variables have a default value of their type depending on the context in which they are used - booleans default to false , integers and floats default to zero, strings (e.g. used in echo ) are set as an empty string and arrays become to an empty array.

Example #1 Default values of uninitialized variables

Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name. E_WARNING (prior to PHP 8.0.0, E_NOTICE ) level error is issued in case of working with uninitialized variables, however not in the case of appending elements to the uninitialized array. isset() language construct can be used to detect if a variable has been already initialized.

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