What impressed me as a beginner in writing Ruby

While creating a portfolio in Ruby Impressed when going back and forth with the basics of Ruby I will summarize how to write Ruby and the rules.

Update from time to time for yourself.

Write variables in snake case

special_price = 200

When using expression expansion, "" double quotes

puts "#{special_price}"

When using single (double) quotes in a string

puts "\"Hello\""
#=> "Hello"

The number _ is ignored

1_000_000_000
#=> 1000000000

For division between integers, the solution is also an integer

1 / 2 #=>0
1.0 / 2 #=>0.5

++ is syntactically invalid

n += 1 #=>2
n *= 3 #=>6
n /= 2 #=>3
n **= 2 #=>9

Rational number

0.1 * 3.0 == 0.3 #=>false
0.1 * 3.0 <= 0.3 #=>false

3/10 instead of decimal with Rational class

0.1r * 3.0r #=>(3/10)

&&Is||More priority

The if statement returns the last evaluated expression

greeting =
    if
        
    elsif
        
    else
        
    end

You can single line your code with if then

if (processing) then (Return value)

%notation

%q!! #=> ' '
%Q!! #=> " "
%!! #=> " "

Here document

a = <<TEXT
String
TEXT

Format string

'%0.3f' % 1.2 #=>"1.200"

Exponential notation

2e-3 #=> 0.002
#2×10^-3

Conditional operator (ternary operator)

message = n > 10 ? 'true' : 'false'

GC (garbage collection)

Collect objects that are no longer in use Automatically release memory

Alias method

Methods of the same implementation with different names

dvimod returns quotients and remainders as an array

14.divmod(3) #=> [4,2]

Omit block arguments if not needed

numbers.each do
    sum += 1
end

You can write ruby code in the block

numbers = [1,2,3,4]
sum = 0
    
numbers.each do |number|
    sum_value = n.even? ? n * 10 : n #Conditional operator
    sum += sum_value #sum_value is valid only within the block
end

sum #=> 64

By the way, when a professional writes it, it's so concise ...! !! !! @scivola, I will study.

numbers = [1,2,3,4]
sum = numbers.sum{ |n| n.even? ? n * 10 : n }

Reference: Array # sum (Ruby 2.7.0 Reference Manual)

Evaluate the elements of the array and make the return value a new array

numbers = [1,2,3,4]
new_numbers = numbers.map { |n| n * 10 }

new_numbers #=> [10,20,30,40]

Method to perform convolution operation

numbers = [1,2,3,4]
sum = numbers.inject(0) { |result, n| result + n }
#1st result result=>0, n=>1, 0+1=1
#2nd result result=>1, n=>2, 1+2=3

sum #=> 10

More concise with the &: method

[1,2,3,4].select { |n| n.odd? } #=> [1,3]
[1,2,3,4].select(&:odd?) #=> [1,3]
#1.When there is only one block argument
#2.When the method has no arguments
#3.Possible when the method is one sentence for the block argument
#&:Operator is useless

Range can also be used for strings

('a'...'e').to_a #=>["a","b","c","d"] ...Does not end

Specify the number of digits

'0'.rjust(5) 		#=> "    0"
'0'.rjust(5, '0')	#=> "00000"

Get the end of an array

a = [1,2,3]
a[-1] #=> 3

Replacement of array elements

a = [1,2,3,4,5]
a[1,3] = 100
#=> [1,100,5]Stupid...

Set of sum and difference products of arrays

a = [1,2,3]
b = [3,4,5]

a | b #=> [1,2,3,4,5]
a - b #=> [1,2]
a & b #=> [3]

Receive all remaining elements as an array with multiple assignment

e, f = 100, 200, 300
e #=> 100
f #=> 200

e, *f = 100, 200, 300
e #=> 100
f #=> [200, 300]

Synthesize the array

a = [1,2]
b = [3,4]

a.push(b) #=> [1,2,[3,4]]
a.push(*b) #=> [1,2,3,4]

Concisely create an array of strings using% notation

['apple', 'melon', 'orange']
#=> ['apple', 'melon', 'orange']

%W!apple melon orange!

%W(apple melon orange)

%W(
	apple
	melon
	orange
)

Initial value of array

a = Array.new(5, 'nil')
#=>[nil, nil, nil, nil, nil]
a = Array.new(5){'default'}
#=>["default", "default", "default", "default", "default"]
#=>All elements are different objects

Join arrays with join

names = ['Sato', 'Tanaka', 'beach']
honorific = names.map{ |name| "#{name}Mr."}
honorific.join('When') #=>"佐藤さんWhen田中さんWhen浜辺さん"

Escape the global area with catch and throw

last_names = ['Sato', 'Tanaka', 'beach']
first_names = ['Taro', 'Jiro', 'Minami']
catch :myfavorite do
    last_names.shuffle.each do |last_name|
        first_names.shuffle.each do |first_name|
            puts "#{last_name} #{first_name}Mr."
            if last_name == "beach" && first_name == "Minami"
				throw :myfavorite #symbol
            end
        end
    end
end