Exactly what is the difference between a "closure" and a "block"?

Question

I've found that lots of people use the words *closure* and *block* interchangeably. Most of these people can't explain what they're talking about. I'm looking for a precise, computer science **definition of a block**, a precise, computer science **definition of a closure** and **clarification on the difference** between the two.

Answer 1

In my experience, closure has a more formal definition in programming languages with first-class functions. In this case, a closure is a structure that stores the function as well as its environment. Its environment consists of the variables used within the function but are defined in some enclosing scope.

In C++, this can be seen with lambdas, where you can explicitly list the environment you capture:

auto my_lambda = [environment_captures, by_value, &by_ref, by_move = std::move(other)](size_t parameters) {

// Function body

};

In Rust, closures are called, well, closures :) and capture implicitly: https://doc.rust-lang.org/book/ch13-01-closures.html

There are many other languages with closures.

Blocks are used to define lexical scopes in a language. The behaviors of a block are defined by the language in question and can change or have exceptions based on name resolution, masking, and hoisting rules of the language. Note that blocks are not strictly associated with functions nor do they require environment capture.

Answer 2

block consists of 3 parts:

1) an opening statement: function name, while loop, for loop, switch statement, etc

2) body : statements inside the block function, loop, selection, etc

3) a CLOSURE, which signals the END of the block

blocks are defined differently depending on the programming language.

For example, in languages like BASIC and PASCAL, blocks are created using BEGIN...END pairs

IN C, C++, java, C#, F# : blocks are created using { and }