Ruby in ten pages: Keywords, identifiers, and basic data types

This is the first page of my Learn Ruby in ten pages project. 

Keywords

These are the reserved words in Ruby:

FALSE	TRUE	__FILE__	__LINE__	alias	and	BEGIN	begin
break	case	class	def	defined?	do	else	elsif
END	end	ensure	for	if	in	module	next
nil	not	or	redo	rescue	retry	return	self
super	then	undef	unless	until	when	while	yield

Identifiers

Variables start with lower-case letter or underscore, constants with upper-case.

Instance variables are prefixed with @

Class variables are prefixed with @@

Global variables are prefixed with $

Class names must be constants (upper case)

Basic data types

Really, there is only one data type in Ruby. Everything is an Object. 

But different objects can exhibit different behaviors. Some of the most common and important are implemented as part of the Ruby language. 

Numbers

Numbers in Ruby are one of three types:

Fixnum: small integer. The range of integers that can be represented is system dependent. On my Macintosh it's -2 ^ 30 to 2 ^ 30 - 1. x.size returns the number of bytes in the binary representation of x.

  

Bignum: big integer. The range of Bignum is practically unlimited. 

Float: floating point number. System dependent. Uses the underlying architecture's floating point representation. 

Expressions involving integers will automatically produce a Fixnum result if Fixnum can represent the value returned; otherwise a Bignum will be returned.

Expressions involving a Float will always return a Float, even if overflow occurs.

Numeric operators are the same for Fixnum and Bignum. 

+ - * /

** exponentiation

% modulo

& | bitwise AND and OR

^ bitwise XOR

<< >> bitwise left/right shift

~x one's complement

-x unary minus

x[n] returns the nth bit of x, where x[0] is the LSB

Bignum binary representation is assumed to be bytewise like Fixnum.

x.coerce(y) returns an array containing compatible values of x and y:

if x and y are the same type, they are stored in the array unchanged.

if x and y are different (e.g., Fixnum and Bignum) an array of two Floats is returned.