In `x = "100".to_i`, the dot sends `to_i` to the string `"100"`. The string is the receiver; the method’s result, integer `100`, is assigned to `x`. Ruby uses this syntax for objects represented by literals as well as variables. section 1.1.4
The dot is Ruby’s message-sending operator: the object on its left receives the message named on its right. Sending a message usually calls a method of that name. The distinction matters because a receiver might not have a matching method. Ruby can handle an unknown message through `method_missing`; the dot alone does not guarantee that a method exists. section 1.1.4 section 2.1.2
Give an object a message to answer
Create an object with `obj = Object.new`, define `def obj.talk; puts "I am an object."; end`, then call `obj.talk`. Here `obj` is the receiver and `talk` names the method it responds to. An argument-bearing call uses the same relationship: `"100".to_i(9)` sends `to_i` to the string with `9` as an argument. section 2.1.2 section 1.1.4
A method call need not show a dot. When the receiver is `self`, Ruby can use it implicitly: inside one instance method, `x` can call another method on the same object. Outside that context, an explicit receiver such as `C.no_dot` may be needed. If a local variable and method share a name, the bare name selects the variable; use `self.talk` or `talk()` to specify the method. section 5.1.4
