Module visibility in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the function accessible outside the module.

Rust

mod greetings {
    pub fn [1]() {
        println!("Hello!");
    }
}

fn main() {
    greetings::hello();
}

Drag options to blanks, or click blank then click option'

Awelcome

Bgreet

Csay_hello

Dhello

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name than the one called in main.

Not making the function public with 'pub'.

The function name must match the call in main. Here, hello is the correct name.

2fill in blank

medium

Complete the code to make the struct field accessible outside the module.

Rust

mod person {
    pub struct Person {
        pub [1]: String,
        age: u32,
    }
}

fn main() {
    let p = person::Person { name: String::from("Alice"), age: 30 };
    println!("Name: {}", p.name);
}

Drag options to blanks, or click blank then click option'

Aperson

Bname

Cinfo

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Making the wrong field public.

Trying to access a private field from outside the module.

The field name must be public to be accessed outside the module.

3fill in blank

hard

Fix the error by completing the code to allow access to the function from outside the module.

Rust

mod utils {
    [1]() {
        println!("Utility function");
    }
}

fn main() {
    utils::helper();
}

Drag options to blanks, or click blank then click option'

Apub fn helper

Bpub helper

Chelper

Dfn helper

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add pub keyword.

Adding pub but missing fn keyword.

The function must be declared as pub fn helper to be accessible outside the module.

4fill in blank

hard

Fill both blanks to make the module and its function accessible from outside.

Rust

mod [1] {
    pub fn [2]() {
        println!("Inside module");
    }
}

fn main() {
    [1]::[2]();
}

Drag options to blanks, or click blank then click option'

Anetwork

Butils

Cconnect

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between module/function names and their usage in main.

Not making the function public.

The module is named utils and the function run is called in main.

5fill in blank

hard

Fill all three blanks to create a public struct with a public method accessible outside the module.

Rust

mod shapes {
    pub struct [1] {
        pub size: u32,
    }

    impl [1] {
        pub fn [2](&self) -> u32 {
            self.size
        }
    }
}

fn main() {
    let s = shapes::[1] { size: 10 };
    println!("Size: {}", s.[2]());
}

Drag options to blanks, or click blank then click option'

ASquare

BCircle

Csize

Dget_size

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for struct or method than in main.

Not making struct or method public.

The struct is named Square and the method get_size returns the size.

Practice

1. What does the pub keyword do in Rust module visibility?

easy

A. Makes a function or item accessible outside its module

B. Makes a function private to its module

C. Deletes the function from the module

D. Renames the function for external use

Solution

1. Step 1: Understand the role of pub

   The pub keyword in Rust is used to make functions, structs, or other items accessible from outside the module they are defined in.

2. Step 2: Contrast with default visibility

   By default, items are private and cannot be accessed outside their module unless marked with pub.

3. Final Answer:

   Makes a function or item accessible outside its module -> Option A

4. Quick Check:

   pub = public access [OK]

Hint: Remember: pub means public, so others can use it [OK]

Common Mistakes:

• Thinking pub hides the item
• Confusing pub with renaming
• Assuming pub deletes the item

2. Which of the following is the correct way to make a struct public in Rust?

easy

A. struct MyStruct { pub field: i32 }

B. struct pub MyStruct { field: i32 }

C. pub struct MyStruct { field: i32 }

D. struct MyStruct pub { field: i32 }

Solution

1. Step 1: Recall correct syntax for public structs

   In Rust, to make a struct public, the pub keyword must come before the struct keyword.

2. Step 2: Check placements of pub

   pub struct MyStruct { field: i32 } correctly places pub before struct. Placing pub inside the braces (on field), writing struct pub MyStruct, or struct MyStruct pub {} are incorrect.

3. Final Answer:

   pub struct MyStruct { field: i32 } -> Option C

4. Quick Check:

   pub struct is correct syntax [OK]

Hint: pub goes before struct, not inside or after [OK]

Common Mistakes:

• Placing pub inside struct braces
• Putting pub after struct name
• Writing pub in the wrong order

3. Given the code:

pub mod outer {
    pub mod inner {
        pub fn greet() { println!("Hello!"); }
    }
}

fn main() {
    outer::inner::greet();
}

What will be the output when this code runs?

medium

A. No output

B. Error: greet is private

C. Error: inner module is private

D. Hello!

Solution

1. Step 1: Check visibility of modules and function

   The outer module is public, containing pub mod inner with pub fn greet(), making them all accessible from main.

2. Step 2: Confirm function call and output

   The call outer::inner::greet() is valid and will print "Hello!" to the console.

3. Final Answer:

   Hello! -> Option D

4. Quick Check:

   pub modules and functions allow access [OK]

Hint: pub on modules and functions means accessible outside [OK]

Common Mistakes:

• Overlooking that the outer module needs pub
• Thinking greet is private by default
• Ignoring nested module visibility

4. What is wrong with this Rust code?

mod my_mod {
    fn secret() {
        println!("Secret function");
    }
}

fn main() {
    my_mod::secret();
}

medium

A. secret function is private and cannot be called from main

B. Missing semicolon after println!

C. Module my_mod is not declared public

D. Function secret must have pub keyword inside main

Solution

1. Step 1: Check function visibility

   The function secret is not marked pub, so it is private to my_mod.

2. Step 2: Understand call from main

   Since main is outside my_mod, it cannot call a private function, causing a compile error.

3. Final Answer:

   secret function is private and cannot be called from main -> Option A

4. Quick Check:

   Private functions can't be accessed outside module [OK]

Hint: Private functions can't be called outside their module [OK]

Common Mistakes:

• Thinking module must be pub to call function
• Assuming missing semicolon causes error
• Believing pub inside main is needed

5. You have a private struct Config inside a module, but want to allow other modules to create instances with limited access to its fields. Which visibility setup is correct?

hard

A. Make struct private and fields public

B. Make struct pub but keep fields private

C. Make both struct and fields private

D. Keep struct private and make fields pub

Solution

1. Step 1: Understand struct and field visibility

   Making the struct pub allows other modules to create instances, but keeping fields private restricts direct access to internal data.

2. Step 2: Evaluate other approaches

   Keeping the struct private (with or without pub fields) prevents other modules from constructing instances. Making everything private blocks access entirely.

3. Final Answer:

   Make struct pub but keep fields private -> Option B

4. Quick Check:

   pub struct + private fields = controlled access [OK]

Hint: pub struct with private fields controls access well [OK]

Common Mistakes:

• Making fields pub but struct private (no instance creation)
• Making everything private (no access)
• Exposing fields unintentionally