What is scope in programming and how does it work?

Scope defines the accessibility of variables, functions, and other identifiers in different parts of a program. It limits the lifetime and accessibility of these elements.

There are different types of scope:

• Local Scope: Variables declared inside a function. Accessible only within that function.
• Global Scope: Variables declared outside any functions or classes. Accessible from any part of the program.
• Block Scope: Variables declared inside a block of code, such as within if, for, or while. Accessible only within that block (in languages supporting block scope, such as Java, Kotlin, C++).

When accessing an identifier, the programming language searches for it "from the inside out": first in the current scope, then in enclosing scopes, and so on up to the global scope. Once the identifier is found, the search stops.

Example in Kotlin:

var globalVariable = "I am global" // Global scope

fun myFunction() {
    var localVariable = "I am local" // Local scope

    if (true) {
        val blockVariable = "I am block" // Block scope
        println(globalVariable) // Access to global
        println(localVariable) // Access to local
        println(blockVariable) // Access to block
    }

    // println(blockVariable) // Error: blockVariable is not accessible outside the block
    println(globalVariable) // Access to global
    println(localVariable) // Access to local
}

fun anotherFunction() {
    println(globalVariable) // Access to global
    // println(localVariable) // Error: localVariable is not accessible outside myFunction
}