What Is the Difference Between a Block, a Proc, and a Lambda in Ruby? (2013)

Summary

What are blocks, procs, and lambdas? Coder Talk: Examples of closures in ruby. Plain old english: Ways of grouping code we want to run. While it looks like these are all very similar, there are subtle differences that I will cover below. Differences between Blocks and Procs 1. Procs are objects, blocks are not A proc (notice the lowercase p) is an instance of the Proc class. This lets us call methods on it and assign it to variables. Procs can also return themselves. In contrast, a block is just part of the syntax of a method call. It doesn’t mean anything on a standalone basis and can only appear in argument lists. 2. At most one block can appear in an argument list In contrast, you can pass multiple procs to methods Differences between Procs and Lambdas Before I get into the differences between procs and lambdas, it is important to mention that they are both Proc objects. However, lambdas are a different 'flavor' of procs. This slight difference is shown when returning the objects. The (lambda) notation is a reminder that while procs and lambdas are very similar, even both instances of the Proc class, they are also slightly different. Below are the key differences. 1. Lamdas check the number of arguments, while procs do not In contrast, procs don't care if they are passed the wrong number of arguments. As shown above, procs don't freak out and raise errors if they are passed the wrong number of arguments. If the proc requires an argument but no argument is passed then the proc returns nil. If too many arguments are passed than it ignores the extra arguments. 2. Lamdas and procs treat the 'return' keyword differently 'return' inside of a lambda triggers the code right outside of the lambda code 'return' inside of a proc triggers the code outside of the method where the proc is being executed So what is a closure? Coder Talk: 'A function or a reference to a function together with a referencing environment. Unlike a plain function, closures allow a function to access...