Quick tour on how Ruby on rails talks to the world

A quick reminder about producing text messages in Ruby.

Talk to the world

The basic method for text output is

puts

from

IO

:

1puts "Hello World"
2# Hello World

With interpolation it's possible to insert some expression in a string:

1age = 2016-1990
2puts "I'm #{age} years old"
3
4# I'm 26 years old

For global, class and instance variables one can omit braces:

1class Person
2  attr_accessor :name
3
4  def hello
5    @@times = 48
6    puts "Hello from #@name, #@@times times in #$0"
7  end
8end
9
10joe = Person.new
11joe.name = "Joe"
12joe.hello
13# Hello from Joe, 48 times in irb

Strings can be concatenated via

+

or

concat

method:

1puts "Hello " + "World"
2
3# Hello World

But we can't do the same with other types:

1age = 2016 - 1990
2puts "I'm " + age + " years old"
3
4# TypeError: no implicit conversion of Fixnum into String

String's

+

uses implicit type conversion using argument's

to_str

method. So we can do the following patching and use numbers in concatenation:

1class Fixnum
2  def to_str
3    self.to_s
4  end
5end
6
7age = 2016 - 1990
8puts "I'm " + age + " years old"
9
10# I'm 26 years old

So if one wants to use a custom class in similar expressions,

to_str

method needs to be added to the class.

Structured Talks

In a number of methods ruby follows some formatting conventions.

printf

prints the string to the output stream using format string,

sprintf

(aliased as

format

) puts the result of formatting in a returned string.

string#%

uses the same format string. The format sequence used there allows developer to control numbers appearence (precision, numeral system) and alignment. It has the following syntax:

%[flags][width][.precision]type

type

defines the general output behavior for an argument (string, number or

#inspect

),

flags

regulate the options and

width~/~precision

set the corresponding appearns options. for the detailed description parameters see

Kernel#sprintf

documentation. Format string content which is not a format sequence is put as is.

1printf "Hello World"
2# Hello World
3printf "Year %d", 2016
4# Year 2016

Let's print some aligned numbers.

%10.2f

stands for 10 position output, 2 digits after dot, right aligned (default):

1printf "Expences:\nJan/02:%10.2f;\nJan/04:%10.2f;", 1234.50, 354.10
2# Expences:
3# Jan/02:   1234.50;
4# Jan/04:    354.10;

Do the same but left aligned (

-

flag) and treat numbers as integers:

1printf "Expences:\nJan/02:%-10d;\nJan/04:%-10d;", 1234.50, 354.10
2# Expences:
3# Jan/02:1234      ;
4# Jan/04:354       ;

String#%

method uses the same format sequence. Applying more than one argument to a format string requires an

Array

.

Hash

can be used for named parameters:

1"Jan/02:%010d" % 1234
2# Jan/02:0000001234
3">%7s: %8.2f" % ["Jan/8", 3425.2399]
4# >  Jan/8:  3425.24
5"Hello %{name}" % { name: 'World' }
6# Hello World

Delivering large messages

Large text also known as

heredoc

can be created the following way. Any identifier (instead of

HEREDOC

below) might be used:

1large_message = <<HEREDOC
2I have something to say.
3...
4But that is quite a long story.
5HEREDOC

Interpolation is allowed, but if you want to disable it put the heredoc identifier in a single quote:

1large_message = <<'HEREDOC'
2I have something to say. #{3+3}
3HEREDOC
4
5puts large_message
6# I have something to say. #{3+3}