If you are familiar with a true object-oriented language like Smalltalk (rather than the watered-down form of OO in C++, Java, etc.), an integer like 5 having methods makes sense because it (like everything else) is an object. Objects in Ruby aren't just window dressing -- they are its core.
In Smalltalk those methods don't return `true`. They take a block and evaluate it if the boolean receiving the message
(a > b) ifTrue: [ "do something" ]
There's no `if` keyword in the language. Control flow is done purely through polymorphism.
I apologize for my lack of Smalltalk knowledge. As you can imagine, you can do similar in Ruby by defining ifTrue to accept a block, even adding ifTrue on other all objects and defining something similar:
class TrueClass
def ifTrue(&block) = block.call
end
class FalseClass
def ifTrue(&block) = nil
end
class Object
def ifTrue(&block) = block.call
end
class NilClass
def ifTrue(&block) = nil
end
problem is not with ifTrue, and not with it's performance, it's easy to do. it is "ifTrue:ifFalse:"
also it is common to do assignments in the "if", and with actual method and blocks scope of the introduced variable would be different and everyone would be tripping on it all the time.
basically it's because of "else" and "elsif". While ".each" works the same as "for .. in ...; end", it's harder to do "if else" as method which will also return value of the block inside the branch. Smalltalk can do it because "ifTrue:ifFalse:" is _one_ message, ruby didn't go that way syntactically.
But then Ruby only goes half way, not unlike the "watered-down form" in your term. Why is `#times` a method of Integer, but `#if` (or `#ifTrue`) not a method of booleans like in Smalltalk? Ruby does the same cherry picking from Smalltalk like everybody else, just different cherries. When looking at Ruby, it feels like the simple examples are all nice and clean but then the weird details start to appear and the language feels more hacky than others (like Ned Flander's house in Simpsons S08E08).