Add information about type hierarchy

Day_1/Day_1.jl

@@ -318,33 +318,33 @@ In Julia, indexing starts with 1️⃣
 # ⚠️ This results in an error!
 # first_vector[0]
 
+# ╔═╡ 7c00f22c-860f-4bb1-b4b4-74c5c3c70f45
+# Last element
+first_vector[end]
+
 # ╔═╡ 45b64c7a-850b-402c-b7ce-2a0bf6d77060
-# ⚠️ No negative indexing, too!
+# ⚠️ No negative indexing!
 # first_vector[-1]
 
 # ╔═╡ d1ed1515-cd59-4e10-a15c-b64325bc44c2
 # Instead, this can be used
 first_vector[end-1]
 
-# ╔═╡ 7c00f22c-860f-4bb1-b4b4-74c5c3c70f45
-# Last element
-first_vector[end]
-
 # ╔═╡ 6c80e009-30de-4232-9a1b-ac954242a5a6
 md"""
 ### Slicing
 """
 
 # ╔═╡ b1426df5-a083-4977-a72c-81e03fd7719d
-# start:end
+# Syntax: start_index:end_index
-first_vector[2:end]
+first_vector[2:4]
 
 # ╔═╡ 5b16ca43-1f56-4934-a420-5ffa5ed437ec
-# start:step:end
+# start_index:step:end_index
 first_vector[1:2:end]
 
 # ╔═╡ 628852dc-16e5-4a03-93a9-be209b1e8fb4
-# List of indices
+# Vector of indices
 first_vector[[1, end, 2]]
 
 # ╔═╡ 3ea54f0d-2aa5-47a3-bbc3-92023a56b834
@@ -352,6 +352,13 @@ md"""
 ### Mutation
 """
 
+# ╔═╡ 6fdc6add-a478-4707-876b-cf6d660870ba
+md"""
+From now on, blocks will be used sometimes when manipulating an array to prevent dependency on execution order.
+
+A block starts with `begin` and ends with `end`. Code in the block should be indented.
+"""
+
 # ╔═╡ e9e117af-1194-4d64-94a8-3e9fd51498aa
 # Setting the first element to 3
 begin
@@ -368,9 +375,11 @@ third_vector = [1, 2, 3]
 # third_vector[2] = 42.1
 
 # ╔═╡ 65d3ddc2-36ed-4126-9211-e838ffc0d859
+# This is because the type of the array is Int64, a Float64 can not be inserted! All elements of an array have to have the same type!
 typeof(third_vector)
 
 # ╔═╡ 641e8c05-3e80-47e5-be77-91090a5f799a
+# You can mix types during initialization of an array
 begin
 	mixed_vector = ["hi", 2.1, 55.7]
 	mixed_vector[2] = 1 + 2im
@@ -378,8 +387,36 @@ begin
 end
 
 # ╔═╡ 2b9a5867-ca82-4a27-a700-bd0bd6c89bbe
+# But then, the type of the array is Any
 typeof(mixed_vector)
 
+# ╔═╡ 944e2d37-8280-47b8-b874-97221955d048
+md"""
+`Any` is the *abstract* type of everything.
+
+Julia does have abstract types which are helpful for multiple dispatch. More about multiple dispatch later 😉
+"""
+
+# ╔═╡ 23d4ac67-05ec-4b3d-8368-86256076be62
+# The type hierarchy
+supertypes(Int64)
+
+# ╔═╡ 866edf5e-a76c-448d-98e8-925eaed5eba5
+subtypes(Number)
+
+# ╔═╡ a8ea4ac1-7f62-4485-a8c5-8ccf00c45720
+subtypes(Real)
+
+# ╔═╡ 786a96be-16cd-4f1b-9b5f-138e232d3183
+subtypes(Integer)
+
+# ╔═╡ dd8dad86-6bc2-4489-8469-7eac80fc41bb
+subtypes(Signed)
+
+# ╔═╡ c336d5f6-80ee-4994-a55f-2d6b3aa3d559
+# Hierarchy of Float64
+supertypes(Float64)
+
 # ╔═╡ 87b43f26-7437-4ee9-9b83-5b21e86dd0c9
 md"""
 ⚠️ Try to avoid using mixed arrays (type `Any`)!
@@ -761,20 +798,28 @@ uuid = "3f19e933-33d8-53b3-aaab-bd5110c3b7a0"
 # ╠═8c47710f-1ed2-40fd-9290-374b498380e3
 # ╟─a03b46cc-1b26-44c2-b83d-884e3dbbe4fa
 # ╠═68658408-188e-43f7-ad74-251172dec0a8
+# ╠═7c00f22c-860f-4bb1-b4b4-74c5c3c70f45
 # ╠═45b64c7a-850b-402c-b7ce-2a0bf6d77060
 # ╠═d1ed1515-cd59-4e10-a15c-b64325bc44c2
-# ╠═7c00f22c-860f-4bb1-b4b4-74c5c3c70f45
 # ╟─6c80e009-30de-4232-9a1b-ac954242a5a6
 # ╠═b1426df5-a083-4977-a72c-81e03fd7719d
 # ╠═5b16ca43-1f56-4934-a420-5ffa5ed437ec
 # ╠═628852dc-16e5-4a03-93a9-be209b1e8fb4
 # ╟─3ea54f0d-2aa5-47a3-bbc3-92023a56b834
+# ╟─6fdc6add-a478-4707-876b-cf6d660870ba
 # ╠═e9e117af-1194-4d64-94a8-3e9fd51498aa
 # ╠═027313d6-c247-43e9-872b-c3f0fe71b733
 # ╠═e77e7ceb-31e3-4231-9923-f62b1382a2d1
 # ╠═65d3ddc2-36ed-4126-9211-e838ffc0d859
 # ╠═641e8c05-3e80-47e5-be77-91090a5f799a
 # ╠═2b9a5867-ca82-4a27-a700-bd0bd6c89bbe
+# ╟─944e2d37-8280-47b8-b874-97221955d048
+# ╠═23d4ac67-05ec-4b3d-8368-86256076be62
+# ╠═866edf5e-a76c-448d-98e8-925eaed5eba5
+# ╠═a8ea4ac1-7f62-4485-a8c5-8ccf00c45720
+# ╠═786a96be-16cd-4f1b-9b5f-138e232d3183
+# ╠═dd8dad86-6bc2-4489-8469-7eac80fc41bb
+# ╠═c336d5f6-80ee-4994-a55f-2d6b3aa3d559
 # ╟─87b43f26-7437-4ee9-9b83-5b21e86dd0c9
 # ╠═22f5ebc1-fd5c-4ee7-b169-8144fbd9b570
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