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Ruby Programming
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Looking Inside Objects

Once you've found an interesting object, you may be tempted to find out just what it can do. Unlike static languages, where a variable's type determines its class, and hence the methods it supports, Ruby supports liberated objects. You really cannot tell exactly what an object can do until you look under its hood.[Or under its bonnet, for objects created to the east of the Atlantic.]

For instance, we can get a list of all the methods to which an object will respond.

r = 1..10 # Create a Range object
list = r.methods
list.length 60
list[0..3] ["size", "end", "length", "exclude_end?"]

Or, we can check to see if an object supports a particular method.

r.respond_to?("frozen?") true
r.respond_to?("hasKey") false
"me".respond_to?("==") true

We can determine our object's class and its unique object id, and test its relationship to other classes.

num = 1 3
num.class Fixnum
num.kind_of? Fixnum true
num.kind_of? Numeric true
num.instance_of? Fixnum true
num.instance_of? Numeric false

Ruby Programming
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  Published under the terms of the Open Publication License Design by Interspire