Ruby speed starter

Because I need to use Ruby and Rails for my work, I spent some time to learn it quickly during the Dragon Boat Festival holiday. Here’s a quick note.

Underlying data types

In Ruby, everything is an object. Each object has a unique object identifier (abbreviated object ID)

Integer type (numbers)

Integers are objects of the Fixnum and Bignum classes. Fixnum objects can hold integers one bit less than the native byte length. When a Fixnum exceeds this range, it is automatically converted to a Bignum object, whose range of representations is limited only by the size of available memory. If the result of an operation on a Bignum object can be represented as Fixnum, the result will be returned as Fixnum

An integer consists of an optional symbolic mark, an optional base indicator (0 for octal, 0d for decimal, 0x for hexadecimal, and 0b for binary), and a string of corresponding bases. Underscores in numeric strings are ignored
```
123456 = > 123456# Fixnum
0d123456                => 123456               # Fixnum123 _456 = > 123456# Fixnum - Ignore underscores- = > 543-543# Fixnum - negative number
0xaabb                  => 43707                # Fixnum - hexadecimal0377 = > 255# Fixnum - octal
-0b10_1010              => -42                  # Fixnum - binary (negative)123 _456_789_123_456_789 = > 123456789123456789# Bignum
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```
Floats (floats)

A numeric literal with a decimal point or exponent is considered a Float object, which is the same size as the double data type on the local machine. There must be at least one digit before and after the decimal point. A string like 1.e3 will attempt to call the e3 method of the Fixnum class
```
12.34 => 12.34-0.1234e2 => -12.34 1234E-2 => 12.34Copy the code
```

String (strings)

Ruby provides a variety of mechanisms for generating literal strings. Each mechanism produces objects of type String. The difference between the different mechanisms is how do you separate strings and what substitutions do you make in literal content

String literals with single quotes perform the fewest substitutions. Examples include ‘stuff’ and %q/stuff/, both of which convert \\ to a single backslash and \’ to single quotes. All other backslashes are not converted

'hello'                     => hello
'a backslash \'\ \ \' '        => a backslash '\'
%q/simple string/           => simple string
%q(nesting (really) works)  => nesting (really) works
%q no_blanks_here ;         => no_blanks_here
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Double quoted strings such as “stuff”, %Q/stuff/ and %/stuff/ also perform additional substitutions

a = 123
"\123mile"                  => Smile
"Say \"Hello\""             => Say "Hello"
%Q!"I said 'nuts',"I said! = >"I said 'nuts'," I said
%Q{Try #{a+1}, not #{a-1}} => Try 124, not 122
%<Try #{a+1}, not #{a-1}> => Try 124, not 122
"Try #{a+1}, not #{a-1}"    => Try 124, not 122
%{#{ a=1; b=2; a+b }} => 3
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Interval (ranges)

The interval uses the expression expr.. Expr and expr… Expr to build Range objects. The form of two points is the closed interval (including the value on the right), while the form of three points is half open and half closed (excluding the value on the right).
```
> (1.. 5).each {|n| puts n} 1 2 3 4 5 > (1... 5).each {|n| puts n} 1 2 3 4Copy the code
```

Array (arrays)

Array class literals are a comma-separated series of object references between square brackets. Trailing commas are ignored. Arrays can also be formed with the abbreviations %w and %w

Arr = [: Fred, 10, 3.14,"this is a string"."pebbles", ]
        => [:fred, 10, 3.14, "this is a string"."pebbles"]

arr = %w( fred wilma barney betty great\ gazoo )
        => ["fred"."wilma"."barney"."betty"."great gazoo"] arr = %w( Hey! \tIt is now -#{Time.now}-)= > ["Hey! \\tIt"."is"."now"."-\#{Time.now}-"] arr = %W( Hey! \tIt is now -#{Time.now}-)= > ["Hey! \tIt"."is"."now"."- the 2019-06-09 11:35:50 + 0800 -"]
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Array objects can access individual elements by providing an index between square brackets. Ruby’s array index starts from zero

a = [1, 'cat', 3.14] = > a three element array [0] = > 1 a [2] = nil = > set a third element = > [1,"cat", nil]
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Hash table (hashes)

Ruby Hash literals consist of a list of key/value pairs in curly braces, separated by commas, and separated by => sequences. Trailing commas are ignored. All keys and values in a specific hash table are not required to be of the same type. The key in the hash table must be able to respond to the hash message and return a hash code, and the hash code corresponding to the key cannot be changed. The keys in the hash table must also be eQL. To compare
```
colors = {
  "red"   => 0xf00,
  "green" => 0x0f0,
  "blue"  => 0x00f,
}
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```
Hash tables are also indexed using the same square bracket notation as arrays
```
colors["red"]           => 3840
colors["white"] = 0xfff => 4095
colors                  => {"red"= > 3840,"green"= > 240,"blue"= > 15,"white"= > 4095}Copy the code
```
Symbol (symbols)

Ruby’s symbol is an identifier that corresponds to a string (usually a name). You can construct the symbol for a name by prefixing it with a colon, or you can create the symbol for any string literal by prefixing it with a colon. Substitution occurs in double-quoted strings. No matter how the program uses names, a specific name or string always produces the same symbol, right
```
:Object
:my_variable
:"Ruby rules"
a = 'cat'
:'catsup'       => :catsup
:"#{a}sup"      => :catsup
:'#{a}sup'= > :"\#{a}sup"
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```
Other languages call this process interning and the symbols atoms
Regular expressions

Regular expression literals are objects of type Regexp. Regular expressions can be created either explicitly by calling the regexp. new constructor, or implicitly using the literal form /pattern/ and %r{pattern}
```
/pattern/
/pattern/options
%r{pattern}
%r{pattern}options
Regexp.new('pattern' [, options])
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```
Once you have a regular expression object, you can use Regexp#match(string) or the match operators =~(must match) and! ~(negative match) matches a string
```
name = "Fats Waller"
name =~ /a/             => 1
name =~ /z/             => nil
/a/ =~ name             => 1
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```
The match operators have the side effect of setting some Ruby variables. $& gets the part of the string that matches the pattern, $’ gets the part of the string that matches before, and $’ ‘gets the part of the string that matches after
```
$& => A pattern matches the string $' => F pattern matches the previous string $'=> ts Waller pattern matches after the stringCopy the code
```

Variables and Constants

Ruby names are used to refer to common, variable, method, class, and module names. The first character must be an uppercase letter, lowercase letter, or underscore, followed by any combination of uppercase letter, lowercase letter, underscore, or digit

Local variable name

A character combination consisting of lowercase letters followed by names. In general, use underscores instead of camelCase for multi-word names
```
three_two_one = 321
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```
Instance variable name

It starts with an @ followed by a name. It’s a good idea to use lowercase after the @
```
@name   @_    @size
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```
Class variable name

It starts at @@, followed by a name
```
@@name  @@_   @@size
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```
Name of a const variable

Start with a capital letter followed by multiple nomenclature characters. Class names and module names are constants, so follow the naming tradition of constants. Traditionally, constant object references are made up of uppercase letters and underscores, while class and module names are mixedcases
```
Module Math ALMOST_PI = 22.0/7.0 end Class BigBlob endCopy the code
```
Global variable names

Consists of the dollar character $followed by the naming character. Global variables can be modified anywhere in the program and are generally not recommended
```
$temp = "this is a global variable"
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```
Multiple assignments

Ruby can assign values to a group of variables simultaneously. If the variable is preceded by *, Ruby will wrap the unallocated value as an array and assign it to the variable
```
A, b, c = 1, 2, 3 a, b, c = 1, 2, 3, 4, 5 = > a = 1, b = 2, c = (three, four, five), a * b, c = 1, 2, 3, 4, 5 = > a = 1, b = [4] 2, c = 5Copy the code
```

conditional

Conditional and true and false

In Ruby, only false and nil are false, and all other values represent true. In addition, there is a general rule in Ruby that, in order to make programs easy to understand, all methods that return true and false should be called? At the end
Logical operator

In Ruby logical operators &&, | | and! , as well as the same but slightly lower priority logical operators and, or, not. Usually the former is used for logical judgment and the latter for process control

Condition 1 and condition 2 must both be true, and the expression returns true
```
Condition 1 &condition 2 condition 1 and condition 2Copy the code
```
If either condition 1 or condition 2 is true, the expression returns true
```
Condition 1 | | conditions condition 1 or 2Copy the code
```
Takes the opposite condition and returns the opposite logic of the conditional expression
```
! Condition not conditionCopy the code
```
Comparison operator

Ruby’s syntax defines the comparison operators ==, ===, <=>, <, <=, >, >=, =~. All of these operators are implemented by methods. Traditionally, Ruby also uses the standard method EQL? And equal? . Where == and =~ have opposite forms! = and! ~

If statement

The if statement is the most basic condition statement of the form:

ifCondition 1thenProcessing 1 Elseif condition 2thenProcessing 2 Elseif condition 3thenTo deal with 3elseDeal with 4 endCopy the code

You can omit then

Unless the statement

Unless is the opposite of if, with the form:
```
Unless conditionsthenDeal with 1elseDeal with 2 endCopy the code
```
You can omit then
The if and unless decorators

If and unless can be written after the code you want to execute, as follows
```
puts "a > b" if a > b
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```
When using modifiers, pay attention to program readability
Ternary operator

The ternary operator is if… Else short form
```
Conditions? Process 1: Process 2Copy the code
```
A case statement

Using a case statement makes the program simpler and easier to understand when there is only one comparison object that performs different processing depending on the value of the object
```
caseThe comparison object when is 1thenProcess 1 when value 2thenProcess 2 when value 3thenTo deal with 3elseDeal with 4 endCopy the code
```
You can omit then

cycle

Times method

The Times method makes it easy to simply perform processing a certain number of times
```
Number of cycles. TimesdoWant the loop to handle endCopy the code
```
do… The end part can be used with {… } instead of
```
Times {desired loop processing}Copy the code
```
The Times method also tells you the current number of cycles in the block
```
5.times do |i|
  puts "Loop #{I}"
end
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```

For statement

For is not a method, but a loop control statement provided by Ruby. The form is as follows:

forvariableinStart value.. The end valuedoWant the loop to handle endforvariableinobjectdoWant the loop to handle endCopy the code

You can omit the do

sum = 0
for i in1.. 5 sum = sum + i end puts sum names = ["awk"."Perl"."Python"."Ruby"]
for name in names
  puts name
end
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While statement

No matter what type of loop, a while statement can do the job. The structure of a while statement is as follows:
```
whileconditionsdoWant the loop to handle endCopy the code
```
You can omit the do
```
i = 1
while i < 3
  puts i
  i += 1
end
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```
Until the statement

Until is the opposite of while. The structure of the until statement is exactly the same as that of the while statement, except that the condition judgment is reversed and the loop is executed only when the condition is not met
```
Until conditionsdoWant the loop to handle endCopy the code
```
You can omit the do
```
sum = 0
i = 1
until sum >= 50
  sum += i
  i += 1
end
puts sum
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```
Each method

The each method fetches objects from a collection of objects one by one, much like a for loop fetches elements from an array
```
Object.do| | variable hope circulation processing end object. Each {| | variable hope circulation processing}Copy the code
```
Inside Ruby, the for statement is implemented using the each method. So you can use an object of the each method, and you can also specify a loop object for the for statement
```
sum = 0 (1.. 5).eachdo |i|
  sum = sum + i
end
puts sum
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```
Loop method

There is also a looping method, where there is no condition to terminate the loop, but just loop processing
```
loop doWant the loop to handle endCopy the code
```
A program accidentally executes an infinite loop, which can be forcibly terminated by Ctrl + C
```
loop do
  puts "Ruby"
end
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```
Cycle control

Break Terminates the processing and breaks the loop

Next skips to the next loop

Redo was repeated under the same conditions. Rarely used in general

methods

call

Simple method calls
```
Object. Method name (parameter 1, parameter 2... , the parameter n)Copy the code
```
Objects are also called receivers. In the object-oriented world, calling a method is called “sending a message to an object.” The result of the call is “the object receives the message.” In other words, a method call is a process in which several parameters are sent to an object along with a message

Method calls with blocks
```
Object. Method name (parameter,...)do| variables 1, 2,... | block content end object. Method name (parameter,...) {| variables 1, 2,... } | piece of contentCopy the code
```
| to | in the specified variables called blocks. During block execution, block variables are passed inside the block by methods
```
5.times do |i|
  puts i
end
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```

define

Definition of general methods

Def method name (arguments 1, 2... , argument n) the processing end that you want to executeCopy the code

We can specify the return value of a method with a return statement

return 值
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Usually the result of the last expression of a method becomes the return value of the method, so you can omit the return statement

With the yield keyword we can define methods with blocks

def myloop
  while true
    yield
  end
end

num = 1
myloop do
  puts "num is #{num}"
  break if num > 10
  num *= 2
end
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A method with an indeterminate number of arguments can be defined by the * variable name. Arguments can also be specified as an array of *

def foo(*args)
  args
end

p foo(1, 2, 3)      => [1, 2, 3]
p foo(*[4, 5, 6])   => [4, 5, 6]
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Defines methods that take keyword arguments

Def method name (parameter 1: the value of parameter 1, parameter 2: the value of parameter 2,...) The processing end that you want to executeCopy the code

The parameter value can be omitted if there is no default value. We can also use the form **args to receive undefined parameters

def volume(x:, y: 2, z: 4, **args)
  [x, y, z, args]
end

p volume(x: 2, y: 3)        => [2, 3, 4, {}]
p volume({x: 3, k: 5})      => [3, 2, 4, {:k=>5}]
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Classes and objects

Class and inheritance

Classes represent classes of objects, and objects in Ruby must all belong to a class. Creating a new class by extending a defined class is called inheritance.
```
Class Class name [< superclass name] Class definition endCopy the code
```
The first letter of a class must be capitalized. The Initialize method in the class is special. When the new method is used to generate a new object, the Initialize method is called and the parameters of the new method are passed to the Initialize method unchanged
```
class HelloWrold
  def initialize(myname = "Ruby")
    @name = myname
  end
end

bob = HelloWrold.new("Bob")
ruby = HelloWrold.new
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```
accessor

In Ruby, instance variables cannot be directly accessed or modified from outside the object; you need methods to access the inside of the object. Ruby provides easy methods to define attr_reader, attr_writer, and attr_accessor

Attr_reader :name read-only (define the name method)

Attr_writer :name only writes (define name= method)

Attr_accessor :name Reads and writes (define both methods)

Class method

Methods whose recipients are the classes themselves are called class methods

The class << class name method defines the end def class name. Method name (parameter,...) endCopy the code

Four definitions are shown below

class << HelloWorld
  def hello(name)
    puts "#{name} said hello."
  end
end

HelloWorld.hello("John")        => John said hello.

class HelloWorld
  class << self
    def hello(name)
      puts "#{name} said hello."
    end
  end
end

HelloWorld.hello("Allen")       => Allen said hello.

def HelloWorld.hello(name)
  puts "#{name} said hello."
end

HelloWorld.hello("Amber")       => Amber said hello.

class HelloWorld
  def self.hello(name)
    puts "#{name} said hello."
  end
end

HelloWorld.hello("Chloe")       => Chloe said hello.
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Class variables and constants

Class variables are shared by all instances of the class, similar to constants

class HelloWorld
  Version = "1.0"
  @@count = 0

  def self.count
    @@count
  end

  def initialize(myname = "Ruby")
    @name = myname
  end

  def hello
    @@count += 1
    puts "Hello, world. I am #{@name}."
  end
end

bob = HelloWorld.new("Bob")
alice = HelloWorld.new("Alice")
ruby = HelloWorld.new

p HelloWorld.count      => 0
bob.hello
alice.hello
ruby.hello
p HelloWorld.count      => 3
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Limiting method calls

Public exposes the method externally in the form of an instance method

Private can only call the method as the default receiver

Protected This method can be called as an instance method when in the same class

Class Point attr_accessor :x, :y protected :x=, :y= def initialize(x=0.0, y=0.0) @x, @y = x, y end public def swap(other) tmp_x, tmp_y = @x, @y @x, @y = other.x, other.y other.x, other.y = tmp_x, tmp_yreturnSelf end p1 = point.new (1.0, 2.0) p2 = point.new (3.0, 4.0) p [p2.x, p2.y] p [p2.x, p2.y] p1. Swap (p2) p [p2.x, p2.y] p1. p1.y] p [p2.x, p2.y]Copy the code

Alias with undef

Sometimes we want to alias an existing method, in which case we need to use the alias method
```
aliasThe alias Formerly known asaliasAlias: original nameCopy the code
```
Undef is used to delete defined methods
```
Undef Method name undef: method nameCopy the code
```

The module

Modules are one of Ruby’s features

Module The module defines endCopy the code

Modules cannot have instances, and modules cannot be inherited. If you want to expose methods as module functions for external use, you need to use the module_function method

module HelloModule
  Version = "1.0"

  def hello(name)
    puts "Hello, #{name}"End module_function :hello end p HelloModule::Version => 1.0 HelloModule."Alice"Alice include HelloModule Version => 1.0 Hello ("Alice")              => Hello, Alice
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You can use mix-ins to Mix modules into classes. Use include when defining a class, so that methods and constants in a module can be used by the class

module M
  def meth
    "meth"
  end
end

class C
  include M
end

c = C.new
p c.meth        => meth
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Error and exception handling

Exception handling

Ruby exceptions are objects of Exception or a subclass of it and are written as follows:
```
Begin Indicates the processing that an exception may occur. Rescue Indicates the processing end when an exception occursCopy the code
```
In Ruby, exceptions and their associated information are handled as objects. The exception object can be obtained by specifying the variable name after rescue
```
Begin Indicates that exceptions may occur rescue => End indicates that exceptions occur in variables that reference abnormal objectsCopy the code
```
The exception object method has the class exception type, the Message exception message, and the backtrace exception location

post-processing

The processing that you want to perform regardless of whether an exception occurs is defined in Ruby using the ensure keyword

Begin Process that may occur rescue => Process that occurs when a variable is abnormal Ensure Process that is performed regardless of whether an exception occurs EndCopy the code

retry

After retry is used in rescue, the operations following begin are repeated
```
begin
  io = File.open(file)
rescue
  sleep 10
  retry
end
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```
Rescue the modifier

Rescue, like the if and unless modifiers, has a corresponding modifier
```
Expression 1 rescue expression 2Copy the code
```
If an exception occurs in expression 1, the value of expression 2 becomes the value of the entire expression
```
n = Integer(val) rescue 0
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```
Abnormal complement

If the scope of exception handling is the entire processing of a method, that is, programs within the entire method use BEGIN… If end is enclosed, begin and end can be omitted, and programs of Rescue and Ensure can be directly written
```
The def foo class defines rescue => ensure endCopy the code
```
When multiple types of exceptions exist and need to be handled according to the types of exceptions, multiple rescues can be used to handle them separately
```
Begin Handle exceptions that may occur rescue Exception1, Exception2 => Variable Exception1 Rescue Exception3 => Variable Exception2 Rescue Handle exceptions other than the preceding exceptions endCopy the code
```
Actively throwing an exception

Raise message – Raises a RuntimeError exception and sets the string as the message in the newly generated exception object

Raise Exception class – Raises the specified exception

Raise Exception class, information – Raises the specified exception and sets the string of information in the newly generated exception object

Raise – Raises a RuntimeError outside rescue. When called from rescue, the exception that last occurred is thrown again ($!).

Block (block)

A block is a collection of processes that can be passed along with arguments when a method is called

Control block execution

Like loops, blocks use break, Next, and redo as process control
Encapsulate a block as an object

As mentioned above, you can use the yield keyword when executing a block in a method that receives a block. Ruby can also treat blocks as objects. Once you treat a block as an object, you can execute the block somewhere other than the method that received it, or hand it off to another method for execution

To manipulate a block as an object, we need the Proc object. A typical way to define a Proc object is to call the blocked method proc.new. The program defined in the block is not executed until the call method of the Proc object is called
```
hello = Proc.new do |name|
  puts "Hello, #{name}"
end

hello.call("World")
hello.call("Ruby")
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```
When defining a method, Ruby automatically wraps the block passed in when the method is called as a Proc object if the trailing argument is an & argument
```
def total(from, to, &block)
  result = 0
  from.upto(to) do |num|
    if block
      result += block.call(num)
    else
      result += num
      end
  end
  return result
end

p total(1, 10)                      => 55
p total(1, 10) {|num| num ** 2}     => 385
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```
scope

Namespaces inside the block are shared with namespaces outside the block. Local variables defined outside the block can continue to be used within the block. Well! In short, this makes it easy for Ruby to implement functional closures.
```
def counter
  cnt = 0
  Proc.new do
    cnt += 1
  end
end

c1 = counter
c2 = counter

c1.call         => 1
c1.call         => 2
c1.call         => 3
c2.call         => 1
c2.call         => 2
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```

resources

Ruby’s official website
Ruby documentation

The original link

Underlying data types

Variables and Constants

conditional

cycle

methods

Classes and objects

Error and exception handling

Block (block)

resources

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