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Ruby Language Overview handout #7
Summary of Ruby features
numbers: Integer (3, 802), Float (3.4)
booleans: true, false
strings: "hello", "how are you?"
arrays: [3, 15, "hello", [7, "howdy"], 308.4, true]
ranges: 1..10, 'a'..'z'
hash: {"stuart"=>"reges", "joe"=>"biden", "donald"=>"trump"}
class Foo [< <superclass>]
<definitions>
end
def f(p1, p2, ..., pn)
<body>
end
def f(p1 = v1, p2 = v2, ..., pn = vn)
<body>
end
Syntactic sugar for defining getters and setters:
attr_reader symbol1, symbol2, ..., symbol-n
attr_writer symbol1, symbol2, ..., symbol-n
The constructor for a class always calls a method called initialize.
public/protected/private keywords used inside a class to mean "starting
here, constructs have this kind of access"
instance-variables start with @
class-variables (static variables) start with @@
symbols start with :
if <bool-expr> [then]
<body>
elsif <bool-expr> [then]
<body>
else
<body>
end
while <bool-expr> [do]
<body>
end
for <variable> in <collection> [do]
<body>
end
loop do
<statements>
break if <bool-expr>
<statements>
end
<variable>.<method>(<params>) { <block> }
<variable>.<method>(<params>) do
<block>
end
<block> can begin with |params| and has a sequence of statements
embed an expression to be evaluated in a string:
"text before #{expression to evaluate} text after"
a method takes a block if it includes calls on yield
nil is a special value that represents "no object"
Useful methods
arithmetic: +, -, *, /, %, ** (exponentiation), +=, -=, *=
mathematical: Math.sqrt, Math.sin, Math.cos
relational: <, >, <=, >=, !=, ==
logical: &&, ||, !
conversion: <Integer>.to_f, <Float>.to_i, <Float>.round, <Object>.to_s
random: rand, rand(<integer>)
higher-order: map, filter, find, find_all, any?, all?, inject, reduce
Array/String:
x.length # of elements (also Hash)
x[i] element i (0-based indexing, also Hash)
x[i, n] slice with n elements starting at i
x[i..j] slice with values at index i through j
x << v append v to x
x.sort sort values
x.member? v does it contain v?
x.index v index of v in x
push v appends v to end of array (Arrays only)
pop remove and return top value (Arrays only)
chomp eliminate trailing newline from string (String only)
upcase uppercase version of string (String only)
Input/Output
puts x like Java println
print x like Java print (stay on current output line)
print x, y print multiple values
gets reads a line of input
File.open(s) returns a file object for given file
<file>.gets read a line from file object
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