Structs, Module und Fehler

struct Punkt                    # unveränderlich (immutable)
    x::Float64
    y::Float64
end

mutable struct Konto            # veränderlich
    inhaber::String
    stand::Float64
end

abstract type Form end
struct Kreis <: Form; r::Float64 end
struct Rechteck <: Form; b::Float64; h::Float64 end

flaeche(k::Kreis) = π * k.r^2
flaeche(r::Rechteck) = r.b * r.h
umfang(k::Kreis) = 2π * k.r
umfang(r::Rechteck) = 2 * (r.b + r.h)

p = Punkt(3, 4)
println(p, " ", p.x, " ", typeof(p), " ", fieldnames(Punkt))
k = Konto("Mia", 100.0)
k.stand += 50
println(k.inhaber, " ", k.stand, " ", ismutable(k), " ", ismutable(p))

formen = [Kreis(1.0), Rechteck(3.0, 4.0), Kreis(2.5)]
for f in formen
    println(typeof(f), ": Fläche ", round(flaeche(f), digits = 2), ", Umfang ", round(umfang(f), digits = 2))
end
println(sum(flaeche, formen) |> x -> round(x, digits = 3))
println(sort(formen, by = flaeche) .|> typeof)

# Konstruktoren mit Prüfung und Standardwerten
struct Person
    name::String
    alter::Int
    function Person(name, alter)
        alter < 0 && throw(ArgumentError("Alter darf nicht negativ sein"))
        new(name, alter)
    end
end
Person(name) = Person(name, 18)
println(Person("Tom"), " ", Person("Zoe", 31).alter)
try
    Person("Ben", -5)
catch e
    println(typeof(e), ": ", e.msg)
end

# Parametrische Typen
struct Paar{A, B}
    erstes::A
    zweites::B
end
println(Paar(1, "eins"), " ", typeof(Paar(1.5, :x)))
using Printf
Base.show(io::IO, p::Punkt) = @printf(io, "Punkt(%.1f, %.1f)", p.x, p.y)
println(p, " ", [Punkt(1, 2), Punkt(3, 4)])

function teile(a, b)
    b == 0 && throw(DivideError())
    return a / b
end

try
    println(teile(10, 2))
    println(teile(1, 0))
catch e
    println("Fehler: ", typeof(e))
finally
    println("finally")
end

function lies_zahl(s)
    try
        return parse(Int, s)
    catch e
        e isa ArgumentError || rethrow()
        return nothing
    end
end
println(lies_zahl("42"), " ", lies_zahl("x"))

struct MeinFehler <: Exception
    code::Int
    text::String
end
Base.showerror(io::IO, e::MeinFehler) = print(io, "MeinFehler $(e.code): $(e.text)")
try
    throw(MeinFehler(404, "nicht gefunden"))
catch e
    println(sprint(showerror, e), " | ", e.code)
end

x = tryparse(Float64, "3.5")
println(x, " ", tryparse(Float64, "abc"), " ", something(tryparse(Int, "q"), -1))
@assert 1 + 1 == 2 "Mathe kaputt"
println(isa(try error("boom") catch e e end, ErrorException))
println(try [1, 2, 3][5] catch e typeof(e) end)
println(try sqrt(-1) catch e typeof(e) end)
println(try Int("x") catch e typeof(e) end)
println(try undefined_variable catch e typeof(e) end)
println(try 1 + "a" catch e typeof(e) end)

module Geometrie
export kreisflaeche, PI2

const PI2 = 2π

kreisflaeche(r) = π * r^2
hilfsfunktion(x) = x + 1          # nicht exportiert

end

using .Geometrie                 # lokales Modul: mit Punkt
println(kreisflaeche(2.0) |> x -> round(x, digits = 3), " ", PI2 |> x -> round(x, digits = 3))
println(Geometrie.hilfsfunktion(1))

using Statistics, Random, Dates
println(mean([1, 2, 3, 4]), " ", median([3, 1, 2]), " ", std([2, 4, 4, 4, 5, 5, 7, 9]) |> x -> round(x, digits = 4), " ", var([1, 2, 3, 4]))
Random.seed!(42)
println(length(rand(5)), " ", all(0 .<= rand(100) .< 1), " ", randperm(5) |> sort)
println(Date(2025, 3, 15) + Day(20), " ", dayofweek(Date(2025, 3, 15)), " ", Date(2025, 12, 24) - Date(2025, 3, 15))