How do declarative programming languages manage state?

1 What is state?

State is a term that refers to the data that is stored and manipulated by a program. For example, if you have a counter that increments every time you click a button, the current value of the counter is part of the state of the program. State can also include user input, configuration settings, database records, and any other information that can change during the execution of the program.

2 How do imperative languages manage state?

Imperative languages are those that use explicit commands and statements to tell the computer how to perform a task. For example, in Python, you can write a loop to iterate over a list and print each element:

for x in [1, 2, 3]:
  print(x)        

In this case, the state of the program is determined by the variables, such as x, that store the current values and change as the loop progresses. Imperative languages allow you to modify the state of the program directly, by assigning new values to variables, calling functions, or using operators.

3 How do declarative languages manage state?

Declarative languages are those that use expressions and declarations to describe what the program should do, rather than how to do it. For example, in SQL, you can write a query to select all the records from a table that match a condition: SELECT * FROM users WHERE age > 18; In this case, the state of the program is determined by the data in the table, which is not modified by the query. Declarative languages do not allow you to modify the state of the program directly, but rather rely on external sources, such as databases, files, or user input, to provide the state. Alternatively, some declarative languages use immutable data structures, such as lists, sets, or maps, that cannot be changed once created, and use functions or operators to create new data structures from existing ones.

4 What are the benefits of declarative state management?

Declarative state management offers several advantages over imperative state management, such as simplifying the logic and readability of the code, reducing the risk of bugs and errors, facilitating parallelism and concurrency, and enabling modularity and reusability. This is because declarative state management avoids side effects, loops, and mutations; prevents unwanted changes to the state; and ensures consistency and integrity of the data. Moreover, it allows multiple processes or threads to access the state without conflicts or synchronization issues. As a result, code can be composed of smaller and independent units that can be combined and reused.

5 What are the drawbacks of declarative state management?

Declarative state management has some disadvantages compared to imperative state management, such as requiring more memory and processing power due to the creation of new data structures and relying on external sources for the state. It also limits the control and flexibility of the code by restricting ways to manipulate and update the state, as well as abstracting the details and performance of the underlying implementation. Furthermore, it increases the complexity of the code by introducing new concepts, syntax, and paradigms that are different from conventional, familiar ones.

6 How to choose between declarative and imperative state management?

There is no definitive answer to whether declarative or imperative state management is better or worse for your program. It depends on factors such as the nature and scope of the problem, the requirements and preferences of the users, the resources and constraints of the environment, and the trade-offs and challenges of each approach. Therefore, it is important to understand the pros and cons of both options, and to use the one that best suits your needs and goals.