Namespace declaration syntax in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code with namespaces?

Consider the following PHP code. What will it output when run?

PHP

<?php
namespace MyApp\Utils;

function greet() {
    return "Hello from Utils!";
}

namespace MyApp\Main;

function greet() {
    return "Hello from Main!";
}

use function MyApp\Utils\greet as utilsGreet;

echo greet() . " and " . utilsGreet();

A Hello from Utils! and Hello from Utils!

B Hello from Utils! and Hello from Main!

C Hello from Main! and Hello from Main!

D Hello from Main! and Hello from Utils!

💡 Hint

Remember that the code after the second namespace declaration is in MyApp\Main namespace.

The first greet() call is in MyApp\Main namespace, so it calls MyApp\Main\greet(). The second call uses the alias utilsGreet which points to MyApp\Utils\greet().

❓ Predict Output

intermediate

What error does this PHP namespace code produce?

What error will this PHP code produce when run?

PHP

<?php
namespace MyApp\Tools;

function tool() {
    return "Tool function";
}

A No error, outputs nothing

B Fatal error: Cannot redeclare namespace

C Parse error: syntax error, unexpected 'function' (missing semicolon after namespace)

D Warning: namespace not found

💡 Hint

Check the syntax after the namespace declaration line.

The namespace declaration line must end with a semicolon or a block. Missing semicolon causes a parse error.

❓ Predict Output

advanced

What is the output of this PHP code with multiple namespace declarations?

What will this PHP code output when executed?

PHP

<?php
namespace A {
    const VALUE = 1;
}

namespace B {
    const VALUE = 2;
}

namespace {
    echo A\VALUE . "," . B\VALUE;
}

A 1,2

B 2,1

C VALUE,VALUE

D Parse error

💡 Hint

Constants in namespaces are accessed with backslash and namespace name.

The code prints the VALUE constant from namespace A and then from namespace B separated by a comma.

❓ Predict Output

advanced

What is the output of this PHP code using namespace and class?

What will this PHP code output when run?

PHP

<?php
namespace Outer\Inner;

class Test {
    public function message() {
        return "Inside Inner";
    }
}

namespace Outer;

class Test {
    public function message() {
        return "Inside Outer";
    }
}

namespace {
    $obj1 = new Outer\Test();
    $obj2 = new Outer\Inner\Test();
    echo $obj1->message() . " and " . $obj2->message();
}

A Inside Inner and Inside Outer

B Inside Outer and Inside Inner

C Fatal error: Class not found

D Parse error

💡 Hint

Classes in different namespaces can have the same name.

The code creates objects from two different namespaces and calls their message methods, printing both results.

❓ Predict Output

expert

What is the output of this PHP code with nested namespaces and use statements?

What will this PHP code output when executed?

PHP

<?php
namespace Alpha\Beta {
    class Sample {
        public function getName() {
            return "Alpha\\Beta";
        }
    }
}

namespace Alpha {
    use Alpha\Beta\Sample as BetaSample;

    class Sample {
        public function getName() {
            return "Alpha";
        }

        public function getBetaName() {
            $obj = new BetaSample();
            return $obj->getName();
        }
    }
}

namespace {
    $obj = new Alpha\Sample();
    echo $obj->getName() . " and " . $obj->getBetaName();
}

A Alpha and Alpha\Beta

B Alpha\Beta and Alpha

C Fatal error: Class not found

D Parse error

💡 Hint

The use statement imports Alpha\Beta\Sample as BetaSample inside Alpha namespace.

The Alpha\Sample class calls its own getName() and also creates an object of BetaSample (which is Alpha\Beta\Sample) to get its name.

Practice

1. What is the correct way to declare a namespace in a PHP file?

easy

A. use MyApp;

B. namespace MyApp;

C. package MyApp;

D. module MyApp;

Solution

1. Step 1: Understand PHP namespace declaration

   PHP uses the keyword namespace to declare namespaces at the top of a file.

2. Step 2: Identify the correct syntax

   The correct syntax is namespace MyApp; with a semicolon at the end.

3. Final Answer:

   namespace MyApp; -> Option B

4. Quick Check:

   Keyword 'namespace' declares namespaces [OK]

Hint: Use 'namespace' keyword followed by name and semicolon [OK]

Common Mistakes:

• Using 'package' instead of 'namespace'
• Forgetting the semicolon at the end
• Using 'use' to declare namespace
• Writing 'module' which is not valid in PHP

2. Which of the following is the correct syntax to declare a nested namespace in PHP?

easy

A. namespace MyApp/Utils;

B. namespace MyApp-Utils;

C. namespace MyApp.Utils;

D. namespace MyApp\Utils;

Solution

1. Step 1: Recognize namespace separator in PHP

   PHP uses backslashes (\) to separate nested namespaces.

2. Step 2: Check each option for correct separator

   Only namespace MyApp\Utils; uses backslashes correctly: namespace MyApp\Utils;.

3. Final Answer:

   namespace MyApp\Utils; -> Option D

4. Quick Check:

   Backslash separates nested namespaces [OK]

Hint: Use double backslash \ for nested namespaces [OK]

Common Mistakes:

• Using forward slash / instead of backslash
• Using dot . or dash - which are invalid
• Omitting the semicolon at the end

3. What will be the output of the following PHP code?

<?php
namespace App\Tools;
class Helper {
  public static function greet() {
    return 'Hello from Helper';
  }
}

use App\Tools\Helper;
echo Helper::greet();
?>

medium

A. Hello from Helper

B. Fatal error: Class 'Helper' not found

C. Hello from App\Tools\Helper

D. Syntax error

Solution

1. Step 1: Understand namespace and use statement

   The class Helper is declared inside namespace App\Tools. The use statement imports it so we can call Helper directly.

2. Step 2: Check method call and output

   Calling Helper::greet() returns the string 'Hello from Helper'.

3. Final Answer:

   Hello from Helper -> Option A

4. Quick Check:

   Use imports class, method returns greeting [OK]

Hint: Use imports namespace class to call methods directly [OK]

Common Mistakes:

• Forgetting to use the 'use' statement
• Calling class without full namespace
• Assuming output includes namespace name
• Syntax errors from missing semicolons

4. Identify the error in this PHP namespace declaration:

<?php
namespace MyApp\Utils
class Logger {}
?>

medium

A. Class name Logger is invalid

B. Namespace name cannot contain backslashes

C. Missing semicolon after namespace declaration

D. Namespace must be declared after class

Solution

1. Step 1: Check namespace declaration syntax

   The namespace declaration must end with a semicolon (;).

2. Step 2: Identify missing semicolon

   The code misses the semicolon after namespace MyApp\Utils.

3. Final Answer:

   Missing semicolon after namespace declaration -> Option C

4. Quick Check:

   Namespace declarations require semicolon [OK]

Hint: Always end namespace line with semicolon [OK]

Common Mistakes:

• Omitting semicolon after namespace
• Thinking backslash is invalid in namespace
• Placing namespace after class
• Misnaming classes

5. You want to declare two nested namespaces Company\Project\Module in one PHP file. Which is the correct way to do this?

hard

A. namespace Company\Project\Module;
class Feature {}

B. namespace Company;
namespace Project;
namespace Module;
class Feature {}

C. namespace Company/Project/Module;
class Feature {}

D. namespace Company.Project.Module;
class Feature {}

Solution

1. Step 1: Understand nested namespace declaration

   PHP allows declaring nested namespaces in one line using backslashes.

2. Step 2: Evaluate each option

   namespace Company\Project\Module; class Feature {} correctly declares nested namespaces with backslashes and a semicolon. Separate declarations like namespace Company; namespace Project; namespace Module; class Feature {} place the class in top-level Module, not nested under Company\Project. Using forward slashes or dots as separators is invalid.

3. Final Answer:

   namespace Company\Project\Module; class Feature {} -> Option A

4. Quick Check:

   Nested namespaces use backslashes in one declaration [OK]

Hint: Use one namespace line with backslashes for nesting [OK]

Common Mistakes:

• Declaring multiple namespaces in one file incorrectly
• Using slashes or dots instead of backslashes
• Forgetting semicolon after namespace
• Trying to declare nested namespaces on separate lines