CSC/ECE 517 Fall 2011/ch1 1c cm

Introduction

high-level overview, who we are trying to target

Closures vs. Methods

introduction of the battle of functional versus object oriented history of the closures with scheme and future languages history of OO methods with C++ and other languages

Summary Table

graphical breakdown of the two and the features we think are important for each

Closures

A closure is a block of executable code together with a reference to the local variables in the environment in which it was created. Those local variables are captured by the closure, and their lifetime is extended to be at least as long as the lifetime of the closure. Closures can be created by defining a function within the body of another function. Anonymous functions are usually implemented as closures.

An example of creating a closure in JavaScript. Note that the scope of the parameter n is limited to the inside of the addGen function. However, because addGen returns a closure, that closure has access to n when it is evoked.

function addGen(n) {
    return function (x) {
        return x + n;
    };
}

var add5 = addGen(5);
var add10 = addGen(10);

alert(add5(6));     // 11
alert(add10(6));    // 16

Here is the same example in C#.

public Func<int, int> addGen(int n)
{
    return x => x + n;
}

var add5 = addGen(5);
var add10 = addGen(10);

Console.WriteLine(add5(6));    // 11
Console.WriteLine(add10(6));   // 16

And again in Ruby

def addGen(n)
    Proc.new { |x| x + n }
end

add5 = addGen(5)
add10 = addGen(10)

puts add5(6)      # 11
puts add10(6)     # 16

First-class functions

closures are typically first-class functions (define first-class functions)

Execution-time environment contains free variables

closures capture variables referenced at the time they are created and the lifetime of those captured variables is extended to at least as long as the lifetime of the closure

Methods

methods and classes are associated with object-oriented programming

Instance or static class functions

methods are functions associated with an object

Execution-time environment contains instance or static variables

methods operate on state associated with an object (environment is closed, but defined by the programmer at compile time)