What are 'First-Class' Objects in Programming?

What are "First-Class" Objects?

In the realm of programming languages, "first-class" objects denote entities that possess the same capabilities and usage privileges enjoyed by other entities, such as variables. Unlike their secondary counterparts, first-class objects can be freely created, eliminated, passed around, and returned as values.

Attributes of First-Class Objects

Depending on the language, first-class objects may possess various attributes, including:

• Expressability as anonymous literals
• Storage in variables and data structures
• Existence of an inherent identity
• Equality comparability
• Acceptability as function/procedure parameters
• Returnability as function/procedure results
• Runtime constructibility
• Printable and readable qualities
• Transmissibility across distributed processes
• Storability outside running programs

Examples of First-Class Objects

In Python, functions are first-class objects, allowing them to be passed as arguments to other functions and returned as results. For instance, the following code demonstrates this concept:

def square(x):
    return x ** 2

result = map(square, range(10))
print(list(result))

In contrast, in C , functions are not inherently first-class objects. However, function pointers and lambda expressions provide a means to simulate first-class functions.

First-Class vs. Second-Class Objects

Entities that lack the full capabilities of first-class objects are referred to as second-class objects. Examples of second-class objects in C include functions that cannot be dynamically created.

Objects vs. First-Class Entities

The term "object" may sometimes be used loosely and does not necessarily imply being first-class. However, languages like Python strive to make all entities first-class, allowing for greater flexibility and expressiveness in code.

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