Namespaces

Question 1

What two problems are namespaces designed to solve?

Answer 1

1. Name collisions between code you create and internal PHP classes/functions/constants or third-party classes/functions/constants.
2. Ability to alias (or shorten) Extra_Long_Names designed to alleviate the first problem, improving readability of source code.

Question 2

PHP namespaces provide a way in which to group related…

Answer 2

…classes (including abstracts and traits), interfaces, functions, and constants.

Question 3

What can’t you use as a namespace name?

Answer 3

PHP, php, and compound names starting with these words.

Question 4

Where is a namespace declared?

Answer 4

At the top of the file, before any code, with one exception: the declare keyword. No non-php code can precede a namespace declaration, not even whitespace.

Question 5

Can multiple namespaces be declared in the same file?

Answer 5

Yes. There are two allowed syntaxes, but bracketing the namespaces is the better syntax. However, using multiple namespaces in one file is strongly discouraged.

Question 6

How do you combine global non-namespaced code with namespaced code, in the same file?

Answer 6

To do so, only bracketed namespace syntax is supported. Global code should be encased in a namespace statement with no namespace name:

namespace { //global code
$a = 1;
}

No PHP code may exist outside of the namespace brackets, except for an opening declare statement.

Question 7

What are the three ways to which a class can be referred?

Answer 7

1. Unqualified name: $a = new foo();
2. Qualified name: $a = new subspacename\foo();
3. Fully qualified name: $a = new \currentnamespace\foo();

Question 8

How can you access any global class, function, or constant, within a namespace?

Answer 8

A fully qualified name can be used, such as \strlen() or \Exception or \INI_ALL.

Question 9

What are the two ways that PHP supports for abstractly accessing elements within the current namespace?

Answer 9

The __NAMESPACE__ magic constant, and the namespace keyword.

Question 10

What is the value of __NAMESPACE__?

Answer 10

A string that contains the current namespace name.

Question 11

In global, un-namespaced code, what does __NAMESPACE__ contain?

Answer 11

An empty string.

Question 12

The namespace keyword is the namespace equivalent of the ____ operator for classes.

Answer 12

The namespace keyword is the namespace equivalent of the self operator for classes.

Question 13

What does this code do?

namespace MyProject
namespace\cname::method();

Answer 13

It calls the static method “method” of class MyProject\cname.

Question 14

What is namespace aliasing/importing?

Answer 14

The ability to refer to an external fully qualified name with an alias. It’s like a symlink.

Question 15

What are the three kinds of namespace aliasing or importing?

Answer 15

Aliasing a class name, aliasing an interface name, and aliasing a namespace name.

Question 16

How is aliasing accomplished in PHP?

Answer 16

With the ‘use’ operator.

Question 17

Can you place multiple ‘use’ statements on the same line?

Answer 17

Yes, just separate them with commas.

Question 18

When is namespace importing performed?

Answer 18

At compile time.

Question 19

Are fully qualified names affected by imports?

Answer 19

No, only unqualified and qualified names.

Question 20

When must the ‘use’ keyword be declared?

Answer 20

In the outermost scope of a file (the global scope), or inside namespace declarations.

Question 21

Will included files inherit the parent file’s importing rules?

Answer 21

No.

Question 22

Class names always resolve to…

Answer 22

…the current namespace name.

Question 23

If a namespaced function or constant does not exist, what will PHP do?

Answer 23

It will fall back to a global function or constant.

Question 24

For the purposes of namespace resolution rules, define the 3 different namespace names.

Answer 24

unqualified name: an identifier without a namespace separator, such as Foo
qualified name: an identifier with a namespace separator, such as Foo\Bar
fully qualified name: an identifier that begins with a namespace separator, such as \Foo\Bar or \Foo

Question 25

What are the 6 namespace resolution rules?

Answer 25

1. Calls to fully qualified functions, classes, or constants are resolved at compile-time. For example new \A\B resolves to class A\B.
2. All unqualified and qualified names (not fully qualified names) are translated during compilation according to current import rules. For example, if the namespace A\B\C is imported as C, a call to C\D\e() is translated to A\B\C\D\e().
3. Inside a namespace, all qualified names not translated according to import rules have the current namespace prepended. For example, if a call to C\D\e() is performed within namespace A\B, it is translated to A\B\C\D\e().
4. Unqualified class names are translated during compilation according to import rules (full name substituted for short imported name). For example, if the namespace A\B\C is imported as C, new C() is translated to new A\B\C().
5. Inside a namespace (say A\B), calls to unqualified functions are resolved at run-time. Here is how a call to function foo() is resolved:
6. It looks for a function from the current namespace: A\B\foo().
7. It tries to find and call the global function foo().
8. Inside a namespace (say A\B), calls to unqualified or qualified class names (not fully qualified class names) are resolved at run-time. Here is how a call to new C() or new D\E() is resolved. For new C():
9. It looks for a class from the current namespace: A\B\C.
10. It attempts to autoload A\B\C.

For new D\E():

1. It looks for a class by prepending the current namespace: A\B\D\E.
2. It attempts to autoload A\B\D\E.

Question 26

Understand name resolution examples here: http://php.net/manual/en/language.namespaces.rules.php

Answer 26

http://php.net/manual/en/language.namespaces.rules.php

Question 27

How are namespace names that contain a backslash (like my\name) but do not begin with a backslash resolved?

Answer 27

In 2 different ways:

1. If there is an import statement that aliases another name to “my”, then the import alias is applied to the “my” in my\name.
2. Otherwise, the current namespace name is prepended to my\name.

Question 28

How does an unqualified namespace name (one without a backslash), like Foo resolve?

Answer 28

In 2 different ways:

1. If there is an import statement that aliases another name to Foo, then the import alias is applied.
2. Otherwise, the current namespace name is prepended to Foo.

Question 29

How does an unqualified function name or constant name like Foo resolve?

Answer 29

Function or constant names that do not contain a backslash can be resolved in 2 different ways:

1. First, the current namespace name is prepended to Foo.
2. Finally, if the constant or function name Foo does not exist in the current namespace, a global constant or function Foo is used if it exists.

Question 30

Does PHP allow nesting namespaces?

Answer 30

No.

Question 31

Can functions or constants be imported via the ‘use’ statement?

Answer 31

No. The only elements that are affected by ‘use’ statements are namespaces and class names.

Question 32

What happens when a constant (qualified or unqualified) that contains a backslash, is not found?

Answer 32

A fatal error.

Question 33

What happens when you try to define a namespaced constant with the same name as a built-in constant such as NULL, TRUE, FALSE, ZEND_THREAD_SAFE, or ZEND_DEBUG_BUILD?

Answer 33

A fatal error.