First-class objects (or first-class citizens) in programming refer to entities that can be treated uniformly throughout the programming language. They possess the following capabilities:

1. Passed as Arguments: They can be passed as arguments to functions.
2. Returned from Functions: They can be returned as values from functions.
3. Assigned to Variables: They can be assigned to variables.
4. Stored in Data Structures: They can be stored in data structures like arrays, lists, dictionaries, etc.

Characteristics of First-Class Objects

To understand first-class objects better, consider these characteristics:

1. No Restrictions on Use: First-class objects have no restrictions on their use within the language.
2. Higher-Order Functions: First-class objects enable the use of higher-order functions, where functions can accept other functions as parameters and return them as results.
3. Flexibility in Abstractions: They provide flexibility in creating abstractions and manipulating them.

Functions as First-Class Objects in Scala

In Scala, functions are treated as first-class objects.

// Assigning a function to a variable
val add = (x: Int, y: Int) => x + y

// Passing a function as an argument
def operate(operation: (Int, Int) => Int, a: Int, b: Int): Int = operation(a, b)
println(operate(add, 2, 3)) // 5

// Returning a function from another function
def createMultiplier(factor: Int): Int => Int = (x: Int) => x * factor
val double = createMultiplier(2)
println(double(5)) // 10

Benefits of First-Class Objects

1. Reusability: Code can be reused more effectively by passing functions as parameters or returning them.
2. Modularity: Functions can be composed to create more complex functionality in a modular way.
3. Higher-Order Functions: Enables the use of higher-order functions, which are functions that operate on other functions.
4. Functional Programming: First-class functions are a cornerstone of functional programming, promoting a declarative style of coding.