What is a flyweight?

July 21, 2014

Took me a while to get this one. At first I understood it to mean the following:

We have a fat object. It has lots of sub-objects, strings in it, lots of data, and so on. Maybe we want to skinny it up, especially if we are using that object a lot (we would find ourselves using a lot of memory).

So my initial understanding was that Flyweight pattern is simply skinnying up an object. Take the repeated common parts out of it, and make them references.

By the way, flyweight historically meant the class of boxer that is very light-weight, under 112 lbs.

That initial understanding was 80% of the way there. The only thing left is to understand that with flyweight objects, it is just a cache of those repeated common parts. Let's say one of the properties of an object is a string for its name. We won't allow each object created to have its name bound along with the object, using all that memory. Instead, we will use a method to access and store to the cache for that value. To make this more concrete, see here:

lookupName(name) {
    if name does not exist,
        store it in the cache,
    return the object containing name from cache
}

Contact me at renaissance.nomad (at) google.com