I would highly recommend this video to anyone who is looking for a better understanding of these three topics.
To get started, let’s look at a very basic example of a closure.
This code obviously works, but keep in mind what is really going on here – we are creating a proc which references the name variable. We then execute the block in the context of the run_proc method, where the name variable doesn’t exist! So this little snippet of code is actually doing something really complex.
Ruby actually attaches the name variable to the block which then makes it available when we want to use it! This is called a closure.
Let’s look at another example, using a lambda instead of a proc.
Again, this works as we expected it to – the a variable is attached to the lambda and can be accessed when the lambda is executed. Now we can try something really strange.
What this snippet is illustrating is that Ruby closures actually attach a reference to the variable being used. That’s why we can update the a variable and have the lambda use the updated value – this is actually different to how a number of other languages implement closures. Happy coding.