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copied!<p>An object, at its simplest, is just a collection of state and functions that operate on that state. A closure is also a collection of state and a function that operates on that state.</p> <p>Let's say I call a function that takes a callback. In this callback, I need to operate on some state known before the function call. I can create an object that embodies this state ("fields") and contains a member function ("method") that performs as the callback. Or, I could take the quick and easy ("poor man's") route and create a closure.</p> <p>As an object:</p> <pre class="lang-c# prettyprint-override"><code>class CallbackState{ object state; public CallbackState(object state){this.state = state;} public void Callback(){ // do something with state } } void Foo(){ object state = GenerateState(); CallbackState callback = new CallbackState(state); PerformOperation(callback.Callback); } </code></pre> <p>This is pseudo-C#, but is similar in concept to other OO languages. As you can see, there's a fair amount of boilerplate involved with the callback class to manage the state. This would be much simpler using a closure:</p> <pre class="lang-c# prettyprint-override"><code>void Foo(){ object state = GenerateState(); PerformOperation(()=>{/*do something with state*/}); } </code></pre> <p>This is a lambda (again, in C# syntax, but the concept is similar in other languages that support closures) that gives us all the capabilities of the class, without having to write, use, and maintain a separate class.</p> <p>You'll also hear the corollary: "objects are a poor man's closure". If I can't or won't take advantage of closures, then I am forced to do their work using objects, as in my first example. Although objects provide more functionality, closures are often a better choice where a closure will work, for the reasons already stated.</p> <p>Hence, a poor man without objects can often get the job done with closures, and a poor man without closures can get the job done using objects. A rich man has both and uses the right one for each job.</p>

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