일급 객체 , 일급함수

https://ko.wikipedia.org/wiki/일급_객체

• 클로저 : A closure is a technique used to bind or "capture" variables from its surrounding scope (the environment where it was created). Even when the function executes in a different scope, it retains access to its original scope. This is useful for maintaining state across function calls.
  • 그 스코프 안에 있는 변수들을 묶어 보관하는 테크닉.
  • 다른 스코프안에서 함수가 실행되었을 때에도 기존 스코프(안에 있는 변수로의) 접근이 간으함
  • 여러 함수호출 속에서 상태를 보존하는 데에 유용함.

(cited from fluent python , 311)

• Record of a Function: The closure is essentially a record (or a snapshot) that stores a function along with its environment. The variables of the enclosing scope are packaged with the function, which allows the function to access those variables even after the outer function has finished execution.

  함수의 레코드 : 클로저는 본질적으로 레코드(거나 스냅숏이다) 함수를 그 환경변수로서 보존하는..이 스코프 속에 변수들은 함수와 함께 패키징 되어서, 함수가 이 변수에 그 함수 실행이 끝난 시점에까지도 접근 가능하게 해준다.

클로저는 함수인가 스코프인가?

A closure in programming is not just a function or just a scope—it is actually a combination of both. It fundamentally consists of a function bundled together with a referencing environment for the free variables necessary to support that function. Here’s how that breaks down:

Function

The core of a closure is a function—it has parameters and a body, just like any typical function you might define. What differentiates a closure functionally is its ability to access variables that are not passed in as parameters but are instead captured from the surrounding scope where the closure was defined.

Referencing Environment

The other crucial component of a closure is the referencing environment (or the closure's "scope"). This environment includes any local variables that were in-scope at the time the closure was created and which are used within the closure. This environment travels with the closure, meaning that the closure can be executed in a different context (e.g., in another function or as a callback) and still retain access to these captured variables.

How It Works Together