Functions

Question 1

Can other functions and class definitions appear inside a function?

Answer 1

Yes.

Question 2

What is a valid function name?

Answer 2

A valid function name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.

Question 3

Can functions be referenced before they are defined?

Answer 3

Yes, except when a function is defined conditionally.

Question 4

What is the scope for functions and classes?

Answer 4

All functions and classes in PHP have the global scope.

Question 5

Can you undefine or redefine previously-declared functions?

Answer 5

No.

Question 6

Are function names case-sensitive?

Answer 6

No.

Question 7

Are function arguments passed by value or reference?

Answer 7

Value.

Question 8

How can you allow a function to modify its arguments?

Answer 8

Pass the arguments by reference. To have an argument to a function always passed by reference, prepend an ampersand (&) to the argument name in the function definition.

Question 9

What types are allowed for the default value of functions?

Answer 9

scalars (boolean, integer, float, string), arrays, and null.

It can’t be a variable, a class member, or a function call.

Question 10

When using default arguments, any defaults should be on the ___ side of any non-default arguments.

Answer 10

Right.

Question 11

How do variable-length argument lists in user-defined functions work?

Answer 11

They are implemented using the … token in PHP 5.6 and later, and using the func_num_args(), func_get_arg(), and func_get_args() functions in PHP 5.5 and earlier. It is also possible to add a type hint before the … token. If this is present, then all arguments captured by … must be objects of the hinted class. You may also pass variable arguments by reference by prefixing the … with an ampersand (&).

Question 12

How do variable-length argument lists in user-defined functions work?

Answer 12

They are implemented using the … token in PHP 5.6 and later, and using the func_num_args(), func_get_arg(), and func_get_args() functions in PHP 5.5 and earlier. It is also possible to add a type hint before the … token. If this is present, then all arguments captured by … must be objects of the hinted class. You may also pass variable arguments by reference by prefixing the … with an ampersand (&).

Question 13

What types may be returned in a function with a return statement?

Answer 13

Any type, including arrays and objects.

Question 14

Can a function return multiple values?

Answer 14

No, but it can return an array.

Question 15

How can you return a reference from a function?

Answer 15

Use the reference operator & in both the function declaration and when assigning the returned value to a variable.

Question 16

What are variable functions?

Answer 16

If a variable name has parentheses appended to it, PHP will look for a function with the same name as whatever the variable evaluates to, and will attempt to execute it. Among other things, this can be used to implement callbacks, function tables, and so forth. Object methods can also be called with the variable functions syntax.

Question 17

How can you display which extensions are loaded into PHP?

Answer 17

Call phpinfo() or get_loaded_extensions().

Question 18

What happens if the parameters given to a function are not what it expects?

Answer 18

The return value of the function is undefined. It’s often NULL, but that’s just a convention, and cannot be relied upon.

Question 19

What are anonymous functions?

Answer 19

Also known as “closures”, they allow the creation of functions which have no specified name. They are most useful as the value of callback parameters, but they have many other uses.

Question 20

Can closures be used as the values of variables?

Answer 20

Yes. PHP automatically converts such expressions into instances of the Closure internal class. Assigning a closure to a variable uses the same syntax as any other assignment, including the trailing semicolon.

Question 21

Can closures inherit variables from the parent scope?

Answer 21

Yes. Any such variables must be passed to the use language construct.

Question 22

What is the parent scope of a closure?

Answer 22

The function in which the closure was declared (not necessarily the function it was called from).