Done structs

Day_5/Day_5.jl

@@ -20,56 +20,145 @@ Julia as a functional language does not have classes like in object oriented lan
 
 Using structs, you can define your own types. Structs use type composition. This means that you combine types into a new one.
 
-In Julia, type annotations DO NOT lead to any performance boosts. Structs build an exception! If you are writing a struct, you have to use type annotations with concrete types (not abstract)!
+In Julia, type annotations DO NOT lead to any performance boosts. Structs build an **exception**! If you are writing a struct, you have to use type annotations with **concrete types** (not abstract)!
 """
 
 # ╔═╡ 3e3e324d-5650-4f81-87cf-fb0f6f55d9d1
+# You should not use a struct for a 2D vector. Use Julia's vectors! This is only for demonstration.
 struct Vec2d
 	x::Float64
 	y::Float64
 end
 
 # ╔═╡ 2ab6f97f-8eed-4b86-9eb6-1de88e6c846d
-vec_2d = Vec2d(1.0, 1.0)
+# Define a variable with this type.
+# The order of the arguments is important!
+# The first argument sets the first field (here `x`).
+# The second argument sets the second field and so on.
+vec_2d = Vec2d(1.0, 2.0)
+
+# ╔═╡ c9be354a-d5ef-4c94-ad2f-c2035dc9323f
+# Access a field
+vec_2d.x
+
+# ╔═╡ 48d31ed6-c5b7-4510-9c49-de8a3a8a0fa7
+vec_2d.y
 
 # ╔═╡ 377a9100-efd8-479c-b9f6-68584c886800
+# It is a new type
 typeof(vec_2d)
 
+# ╔═╡ 9940a716-1109-46f9-a88a-29a7a996412d
+md"""
+## Structs with abstract types
+"""
+
 # ╔═╡ 0e62a7b2-0636-4018-b005-0ae674fec45e
 # Wow, we did reach infinity ♾️
+# This is because of the limits of Float64
 Vec2d(factorial(big(1000)), 2.0)
 
+# ╔═╡ 70bb19db-3d97-4ae1-92d8-552574aa53c3
+md"""
+You might think this problem can be fixed by changing the type of the fields from `Float64` to something like `Real`. This will work, but it does harm performance!
+
+**One more important performance tip: Don't use structs with abstract field types (or no types)!**
+"""
+
 # ╔═╡ 6046417c-460b-4b0c-8423-4d6c4c18731f
+# Bad usage of abstract field types
 struct BadVec2d
 	x::Real
 	y::Real
 end
 
 # ╔═╡ 3e21d34f-3758-427f-85c0-7c457f3f0904
+# It does work, but it is bad for performance
 bad_vec2d = BadVec2d(factorial(big(1000)), 2.0)
 
 # ╔═╡ 4a07f5e3-2413-49c4-824c-b9c844695052
+# The type does not say anything about what the fields type is.
 typeof(bad_vec2d)
 
 # ╔═╡ 9008b1c4-ad76-4d4f-b6c5-001a77543b97
+# Better for performance:
+# Use this syntax to let the type be derived from an abstract type
 struct BetterVec2d{T<:Real}
 	x::T
 	y::T
 end
 
 # ╔═╡ 830dd737-4fdc-42c7-b105-d0622b055db1
+# This works too and it is good for performance
 big_vec2d = BetterVec2d(factorial(big(1000)), big(1))
 
 # ╔═╡ f91b0c58-bc44-414a-b357-145d8c4339d2
+# You see that a concrete type was choosen!
 typeof(big_vec2d)
 
+# ╔═╡ 169de33e-cff8-4419-be18-0f487c185ad7
+# The concrete type of the fields is determined on construction
+typeof(BetterVec2d(1.0, 2.0))
+
 # ╔═╡ 3f1b8df9-104b-42c3-97ee-11782f9f744f
+# This will not work. Both fields has to have the same type.
 # BetterVec2d(1.0, 1)
 
+# ╔═╡ a053b367-f7f2-440e-b9e0-4987b491c256
+struct MixedVec2d{T1<:Real, T2<:Real}
+	x::T1
+	y::T2
+end
+
+# ╔═╡ 1eab61c9-74e1-4540-9750-6ec8448e4950
+# This works
+mixed_vec2d = MixedVec2d(1.0, 1)
+
+# ╔═╡ 4a24f24b-d872-4cd8-bf76-49a0496e4ea6
+# Two different concrete types for the fields
+typeof(mixed_vec2d)
+
+# ╔═╡ c9f68fcf-2b20-43b1-839a-59805357c6d3
+md"""
+## Mutation
+By default, structs are not mutable!
+
+If you want to be mutable, you have to use the keyword `mutable`.
+"""
+
+# ╔═╡ f8b27d41-448a-4329-986f-e65e0b3e77d6
+# This will not work because the struct is immutable by default
+# vec_2d.x = 42.0
+
+# ╔═╡ da9e39a5-0ee3-4f6c-8cb1-abb3ebf3a01e
+# Defining a mutable struct
+mutable struct MutVec2d
+	x::Float64
+	y::Float64
+end
+
+# ╔═╡ d16ac12a-c772-4fee-a309-5b4a2708d08e
+begin
+	mut_vec = MutVec2d(1.0, 2.0)
+
+	# Mutating a field
+	mut_vec.x = 42.0
+	
+	mut_vec
+end
+
+# ╔═╡ d635a63b-44d9-4bfc-a873-ef537cdbdb09
+md"""
+## Structs from abstract types
+To use the features of mutliple dispatch, define an abstract type and derive structs from it.
+"""
+
 # ╔═╡ 10c380fd-80e6-4cb7-b50e-1a7998ec00c5
+# Defining an abstract type
 abstract type Student end
 
 # ╔═╡ 58de483d-c2b5-4252-b6da-64bd8bfac1ac
+# Defining a struct derived from the abstract type `Student`
 struct MathStudent<:Student
 	name::String
 	hobby::String
@@ -79,10 +168,11 @@ end
 struct PhysicsStudent<:Student
 	name::String
 	hobby::String
-	favorite_particle::String
+	favorite_particle::String # Some additional field
 end
 
 # ╔═╡ b535fd1d-695d-49fb-8a6a-2f2f0053a6f6
+# Define a function that works on all students
 function print_name(student::Student)
 	println(student.name)
 
@@ -90,17 +180,19 @@ function print_name(student::Student)
 end
 
 # ╔═╡ 63f32169-b98c-4212-bbd9-4c601266f209
+# Define a method that works only with math students
 function print_information(math_student::MathStudent)
 	println("Math student: $(math_student.name)")
-	println("hobby: $(math_student.hobby)")
+	println("Hobby: $(math_student.hobby)")
 
 	return
 end
 
 # ╔═╡ cb49717b-0584-430e-a30c-c4d02cf55eb2
+# Define a method that works only with physics students
 function print_information(physics_student::PhysicsStudent)
 	println("Physics student: $(physics_student.name)")
-	println("hobby: $(physics_student.hobby)")
+	println("Hobby: $(physics_student.hobby)")
 	println("Favorite particle: $(physics_student.favorite_particle)")
 
 	return
@@ -124,10 +216,70 @@ print_information(math_student)
 # ╔═╡ bc8ef92b-1c68-4c9d-948a-6196dcd2b378
 print_information(physics_student)
 
-# ╔═╡ d8a2ae5c-b42a-4673-9a95-24cfc69ea3e7
+# ╔═╡ 06805ff8-f4bc-4779-baa9-2801a44407b6
 md"""
-# Writing documentation
+## Constructors
+You can either define new constructors for a struct or overwrite the default constructor.
+"""
 
+# ╔═╡ d1937187-15b0-46e7-9589-05d2349aa93a
+# `begin` blocks are only needed in Pluto notebooks
+begin
+	struct ComputerScienceStudent<:Student
+		name::String
+		hobby::String
+	end
+	
+	# Defining an additional constructor to the default constructor
+	function ComputerScienceStudent(name)
+		return ComputerScienceStudent(name, "Programming")
+	end
+end
+
+# ╔═╡ 721e268d-b7c5-4ea8-b4d7-2bab6e2a6fb0
+# Using the default constructor
+ComputerScienceStudent("John", "Tennis")
+
+# ╔═╡ 0f76bd6b-906f-49b3-8a36-9e02feb750b9
+# Using the additional constructor
+ComputerScienceStudent("Selina")
+
+# ╔═╡ 513a4b3f-5b12-4d65-9321-0c883f12a1eb
+mutable struct BiologyStudent<:Student
+	name::String
+	hobby::String
+	
+	# Overwriting the default constructor
+	# You have to use the keyword `new`
+	function BiologyStudent(name)
+		return new(name, "Observing animals")
+	end
+end
+
+# ╔═╡ 3063d330-c411-431e-9e7a-eb3f5cd3ee7b
+# This will not work because the default constructor is overritten!
+# BiologyStudent("Kate", "Swimming")
+
+# ╔═╡ 9e621eb5-a163-4a7a-abd5-85bdf9469692
+# The new default constructor
+BiologyStudent("Kate")
+
+# ╔═╡ 44511b7e-a38a-450f-9a55-b6b6a4d3edd5
+# This is the default constructor now
+begin
+	biology_student = BiologyStudent("Kate")
+
+	# The struct has to be mutable
+	biology_student.hobby = "Swimming"
+	
+	biology_student
+end
+
+# ╔═╡ eddfd543-091b-4a32-8124-a67687dcf457
+md"""
+Why would you want to overwrite the default constructor?
+
+It is useful if you want to enforce checking fields before construction.
 """
 
 # ╔═╡ c24c04e4-b131-11ec-2c1b-7de12fe0c324
@@ -187,11 +339,6 @@ md"""
 ## `DifferentialEquations.jl`
 """
 
-# ╔═╡ b621819d-6ce3-41e1-9e61-3ad0a2c9b016
-md"""
-## `Intervals.jl`
-"""
-
 # ╔═╡ 0174178f-3ed9-4890-8482-714cb51a635d
 md"""
 ## `ProgressMeter.jl`
@@ -202,6 +349,11 @@ md"""
 ## `NaturallyUnitful.jl`
 """
 
+# ╔═╡ 097b1b98-8b98-4160-bf31-d982f21ab8d6
+md"""
+## `Symbolics.jl`
+"""
+
 # ╔═╡ 2430f309-be28-4bc2-9692-92489c31f7b2
 md"""
 # Resources
@@ -424,18 +576,31 @@ uuid = "3f19e933-33d8-53b3-aaab-bd5110c3b7a0"
 """
 
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