[crystal/en] Update to Crystal 1.0 (#4235)

Crystal 1.0 was released this year (currently at 1.1.1 actually), which solidified the language. Updating based on language changes.
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Valentin Baca 2021-09-25 08:03:53 -07:00 committed by GitHub
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@ -4,6 +4,7 @@ filename: learncrystal.cr
contributors:
- ["Vitalii Elenhaupt", "http://veelenga.com"]
- ["Arnaud Fernandés", "https://github.com/TechMagister/"]
- ["Valentin Baca", "https://github.com/valbaca/"]
---
@ -64,24 +65,25 @@ true.class #=> Bool
1.5e10.class #=> Float64
1.5e-7.class #=> Float64
# Chars
# Chars use 'a' pair of single quotes
'a'.class #=> Char
# Octal codepoint
'\101' #=> 'A' : Char
# Chars are 32-bit unicode
'あ' #=> 'あ' : Char
# Unicode codepoint
'\u0041' #=> 'A' : Char
# Strings
# Strings use a "pair" of double quotes
"s".class #=> String
# Strings are immutable
s = "hello, " #=> "hello, " : String
s.object_id #=> 134667712 : UInt64
s += "Crystal" #=> "hello, Crystal" : String
s += "Crystal"
s #=> "hello, Crystal" : String
s.object_id #=> 142528472 : UInt64
# Supports interpolation
@ -89,7 +91,8 @@ s.object_id #=> 142528472 : UInt64
# Multiline string
"This is
multiline string"
multiline string" #=> "This is\n multiline string"
# String with double quotes
%(hello "world") #=> "hello \"world\""
@ -110,7 +113,7 @@ sentence == "question?" #=> false : Bool
# Arrays
[1, 2, 3].class #=> Array(Int32)
[1, "hello", 'x'].class #=> Array(Int32 | String | Char)
[1, "hello", 'x'].class #=> Array(Char | Int32 | String)
# Empty arrays should specify a type
[] # Syntax error: for empty arrays use '[] of ElementType'
@ -154,24 +157,24 @@ array.includes? 3 #=> true
# There is a special array syntax with other types too, as long as
# they define a .new and a #<< method
set = Set{1, 2, 3} #=> [1, 2, 3]
set = Set{1, 2, 3} #=> Set{1, 2, 3}
set.class #=> Set(Int32)
# The above is equivalent to
set = Set(typeof(1, 2, 3)).new
set << 1
set << 2
set << 3
set = Set(typeof(1, 2, 3)).new #=> Set{} : Set(Int32)
set << 1 #=> Set{1} : Set(Int32)
set << 2 #=> Set{1, 2} : Set(Int32)
set << 3 #=> Set{1, 2, 3} : Set(Int32)
# Hashes
{1 => 2, 3 => 4}.class #=> Hash(Int32, Int32)
{1 => 2, 'a' => 3}.class #=> Hash(Int32 | Char, Int32)
{1 => 2, 'a' => 3}.class #=> Hash(Char| Int32, Int32)
# Empty hashes should specify a type
{} # Syntax error
{} of Int32 => Int32 # {}
Hash(Int32, Int32).new # {}
# Empty hashes must specify a type
{} # Syntax Error: for empty hashes use '{} of KeyType => ValueType'
{} of Int32 => Int32 # {} : Hash(Int32, Int32)
Hash(Int32, Int32).new # {} : Hash(Int32, Int32)
# Hashes can be quickly looked up by key
hash = {"color" => "green", "number" => 5}
@ -179,6 +182,9 @@ hash["color"] #=> "green"
hash["no_such_key"] #=> Missing hash key: "no_such_key" (KeyError)
hash["no_such_key"]? #=> nil
# The type of the returned value is based on all key types
hash["number"] #=> 5 : (Int32 | String)
# Check existence of keys hash
hash.has_key? "color" #=> true
@ -220,7 +226,7 @@ Range.new(1, 10).class #=> Range(Int32, Int32)
# Access tuple's value by its index
tuple = {:key1, :key2}
tuple[1] #=> :key2
tuple[2] #=> syntax error : Index out of bound
tuple[2] #=> Error: index out of bounds for Tuple(Symbol, Symbol) (2 not in -2..1)
# Can be expanded into multiple variables
a, b, c = {:a, 'b', "c"}
@ -246,7 +252,7 @@ elsif false
"else-if, optional"
else
"else, also optional"
end
end
puts "if as a suffix" if true
@ -314,7 +320,7 @@ if a < 3
else
a = true
end
typeof a #=> (Bool | String)
typeof(a) #=> (Bool | String)
if a && b
# here both a and b are guaranteed not to be Nil
@ -388,15 +394,19 @@ dinner #=> "quesadilla"
5.even? # false
5.odd? # true
# And if a method ends with an exclamation mark, it does something destructive
# like mutate the receiver. Some methods have a ! version to make a change, and
# Also by convention, if a method ends with an exclamation mark, it does
# something destructive like mutate the receiver.
# Some methods have a ! version to make a change, and
# a non-! version to just return a new changed version
company_name = "Dunder Mifflin"
company_name.gsub "Dunder", "Donald" #=> "Donald Mifflin"
company_name #=> "Dunder Mifflin"
company_name.gsub! "Dunder", "Donald"
company_name #=> "Donald Mifflin"
fruits = ["grapes", "apples", "bananas"]
fruits.sort #=> ["apples", "bananas", "grapes"]
fruits #=> ["grapes", "apples", "bananas"]
fruits.sort! #=> ["apples", "bananas", "grapes"]
fruits #=> ["apples", "bananas", "grapes"]
# However, some mutating methods do not end in !
fruits.shift #=> "apples"
fruits #=> ["bananas", "grapes"]
# Define a class with the class keyword
class Human
@ -404,7 +414,7 @@ class Human
# A class variable. It is shared by all instances of this class.
@@species = "H. sapiens"
# type of name is String
# An instance variable. Type of name is String
@name : String
# Basic initializer
@ -469,9 +479,9 @@ class TestClass
end
# Variables that start with a capital letter are constants
Var = "I'm a constant"
Var = "can't be updated" # Already initialized constant Var
Var = "can't be updated" # Error: already initialized constant Var
# Class is also an object in crystal. So class can have instance variables.
# Class is also an object in Crystal. So a class can have instance variables.
# Class variable is shared among the class and all of its descendants.
# base class