In Kotlin, you can use default arguments and named arguments to simplify function calls and make your code more readable and flexible. Here’s how each of them works:

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Default Arguments

• Default arguments allow you to set a default value for a function parameter. If you don’t pass a value for that parameter when calling the function, the default value will be used.
• You define default values by assigning them directly in the function definition.

Example:

fun greet(name: String, greeting: String = "Hello") {
    println("$greeting, $name!")
}

// Usage:
// Default value for "greeting" is used => Output: "Hello, Alice!"
greet("Alice")
// Provided value overrides the default => Output: "Hi, Bob!"
greet("Bob", "Hi")            

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Named Arguments

• Named arguments allow you to explicitly specify which parameter you’re setting a value for, by using the parameter name when calling the function.
• This is particularly useful when a function has many parameters, especially if some of them have default values.

Example:

fun createAccount(username: String, email: String, isAdmin: Boolean = false) {
    println("Username: $username, Email: $email, Admin: $isAdmin")
}

// Usage:
// isAdmin takes the default value => 
// Output: Username: user1, Email: [email protected], Admin: false
createAccount("user1", "[email protected]")
// All arguments provided normally => 
// Output: Username: admin, Email: [email protected], Admin: true
createAccount("admin", "[email protected]", true)
// Named arguments make the order flexible => 
// Output: Username: user2, Email: [email protected], Admin: false
createAccount(email = "[email protected]", username = "user2") 

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Combining Default and Named Arguments

You can combine these features to make function calls more flexible:

Example:

fun printBookInfo(title: String, author: String = "Unknown", year: Int = 2023) {
    println("Title: $title, Author: $author, Year: $year")
}

// Usage:
// Only title is provided; others use defaults
printBookInfo("Kotlin for Beginners")                    
// Output: Title: Kotlin for Beginners, Author: Unknown, Year: 2023

// Override the default value of 'year'
printBookInfo("Advanced Kotlin", year = 2020)            
// Output: Title: Advanced Kotlin, Author: Unknown, Year: 2020

// Arguments in a different order with named arguments
printBookInfo(author = "John Doe", title = "My Journey") 
// Output: Title: My Journey, Author: John Doe, Year: 2023

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Rules and Notes:

• If a parameter has no default value, it must always be passed.
• Once you start using named arguments in a function call, all subsequent arguments should be named as well.
• Named arguments improve clarity in cases of multiple parameters with the same type or where parameter order can be confusing.

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By combining default arguments and named arguments, you can create more flexible, readable, and maintainable functions in Kotlin.