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Ruby Programming
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Top-Level Execution Environment

Many times in this book we've claimed that everything in Ruby is an object. However, there's one thing that we've used time and time again that appears to contradict this---the top-level Ruby execution environment.

puts "Hello, World"

Not an object in sight. We may as well be writing some variant of Fortran or QW-Basic. But dig deeper, and you'll come across objects and classes lurking in even the simplest code.

We know that the literal "Hello, World" generates a Ruby String, so there's one object. We also know that the bare method call to puts is effectively the same as self.puts. But what is ``self''?

self.type Object

At the top level, we're executing code in the context of some predefined object. When we define methods, we're actually creating (private) singleton methods for this object. Instance variables belong to this object. And because we're in the context of Object, we can use all of Object's methods (including those mixed-in from Kernel) in function form. This explains why we can call Kernel methods such as puts at the top level (and indeed throughout Ruby): these methods are part of every object.
Ruby Programming
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  Published under the terms of the Open Publication License Design by Interspire