Add constructors-and-invariants parity module for C#, Go, and Python

Author: lucasbellesi

LANGUAGE_PARITY_MATRIX.md

@@ -42,16 +42,16 @@ Current parity progress in non-C++ tracks:
 
 Current parity progress in non-C++ tracks:
 
-- C#: `1/5` modules complete in `03-advanced`
-- Go: `1/5` modules complete in `03-advanced`
-- Python: `1/5` modules complete in `03-advanced`
+- C#: `2/5` modules complete in `03-advanced`
+- Go: `2/5` modules complete in `03-advanced`
+- Python: `2/5` modules complete in `03-advanced`
 
 ### Advanced (`03-advanced`) - Current Expansion Queue
 
 | Order | Module | C++ | C# | Go | Python |
 | --- | --- | --- | --- | --- | --- |
 | 1 | structs-and-classes | Done | Done | Done | Done |
-| 2 | constructors-and-invariants | Done | Planned | Planned | Planned |
+| 2 | constructors-and-invariants | Done | Done | Done | Done |
 | 3 | copy-and-move-semantics | Done | Planned | Planned | Planned |
 | 4 | inheritance-and-polymorphism | Done | Planned | Planned | Planned |
 | 5 | templates-basics | Done | Planned | Planned | Planned |

README.md

@@ -25,9 +25,9 @@ This repository teaches programming through small runnable examples and focused
 | Language | Current Levels | Module Coverage | Track Status |
 | --- | --- | --- | --- |
 | C++ | 00-setup, 01-foundations, 02-core, 03-advanced, 04-expert | Foundations, Core, Advanced, Expert, projects, assessments | Most complete and primary track |
-| C# | 01-foundations, 02-core, 03-advanced | 8/8 foundations modules, 6/6 core modules, 1/5 advanced modules | Advanced parity pilot in progress |
-| Go | 01-foundations, 02-core, 03-advanced | 8/8 foundations modules, 6/6 core modules, 1/5 advanced modules | Advanced parity pilot in progress |
-| Python | 01-foundations, 02-core, 03-advanced | 8/8 foundations modules, 6/6 core modules, 1/5 advanced modules | Advanced parity pilot in progress |
+| C# | 01-foundations, 02-core, 03-advanced | 8/8 foundations modules, 6/6 core modules, 2/5 advanced modules | Advanced parity in progress |
+| Go | 01-foundations, 02-core, 03-advanced | 8/8 foundations modules, 6/6 core modules, 2/5 advanced modules | Advanced parity in progress |
+| Python | 01-foundations, 02-core, 03-advanced | 8/8 foundations modules, 6/6 core modules, 2/5 advanced modules | Advanced parity in progress |
 
 Parity planning reference: [LANGUAGE_PARITY_MATRIX.md](LANGUAGE_PARITY_MATRIX.md)
 

languages/csharp/03-advanced/README.md

@@ -5,9 +5,10 @@ This level starts advanced object modeling and type design.
 ## Module Order
 
 1. [structs-and-classes](./structs-and-classes/README.md)
+2. [constructors-and-invariants](./constructors-and-invariants/README.md)
 
 Track progress in [../CHECKLIST.md](../CHECKLIST.md).
 
 ## Study Tip
 
-Use `structs-and-classes` first to build clear mental models for value vs reference types before adding more advanced modules.
+Use `constructors-and-invariants` after `structs-and-classes` to enforce object rules consistently from construction to updates.

languages/csharp/03-advanced/constructors-and-invariants/README.md

@@ -0,0 +1,47 @@
+# Constructors and Invariants (C#)
+
+This module shows how constructors enforce valid object state.
+
+## Quick Run
+
+~~~bash
+dotnet run --project example/constructors-and-invariants-example.csproj
+~~~
+
+## Topics Covered
+
+- Constructor guards that normalize invalid inputs.
+- Defining invariants as always-true class rules.
+- Safe update methods that reject invalid transitions.
+- Reporting operation success without breaking object state.
+
+## Common Pitfalls
+
+- Accepting invalid constructor values and fixing later.
+- Updating private state directly from callers.
+- Returning success when an invalid update was ignored.
+
+## Exercise Focus
+
+- exercises/01.cs: bank account with non-negative balance invariant.
+- exercises/02.cs: date model with month/day validation.
+
+### Exercise Specs
+
+1. exercises/01.cs
+- Input: initial balance and transaction values.
+- Output: updated balance with validity checks.
+- Edge cases: negative initial balance; withdrawal beyond balance.
+
+2. exercises/02.cs
+- Input: month and day values.
+- Output: valid/invalid date result.
+- Edge cases: month out of range; day out of range for month.
+
+## Checkpoint
+
+- [ ] I can define clear invariants for a class.
+- [ ] I can enforce invariants in constructors and methods.
+- [ ] I can reject invalid updates safely.
+- [ ] I completed exercises/01.cs.
+- [ ] I completed exercises/02.cs.

languages/csharp/03-advanced/constructors-and-invariants/example/constructors-and-invariants-example.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>disable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>

languages/csharp/03-advanced/constructors-and-invariants/example/main.cs

@@ -0,0 +1,47 @@
+// Example purpose: show the module flow with clear, beginner-friendly steps.
+
+using System;
+
+class Temperature
+{
+    private double celsius;
+
+    public Temperature(double celsiusValue)
+    {
+        // Intent: enforce the invariant at construction time.
+        celsius = celsiusValue < -273.15 ? -273.15 : celsiusValue;
+    }
+
+    public bool SetCelsius(double newValue)
+    {
+        if (newValue < -273.15)
+        {
+            return false;
+        }
+
+        celsius = newValue;
+        return true;
+    }
+
+    public double Celsius => celsius;
+}
+
+class Program
+{
+    static void Main()
+    {
+        // Program flow: construct with invalid input, then apply valid and invalid updates.
+        Temperature temperature = new Temperature(-500.0);
+        Console.WriteLine($"Initial value (clamped): {temperature.Celsius} C");
+
+        bool updated = temperature.SetCelsius(25.0);
+        Console.WriteLine($"Set to 25.0 success: {updated}");
+        Console.WriteLine($"Current value: {temperature.Celsius} C");
+
+        bool rejected = temperature.SetCelsius(-300.0);
+        Console.WriteLine($"Set to -300.0 success: {rejected}");
+
+        // Intent: final state confirms that invariant was preserved.
+        Console.WriteLine($"Current value: {temperature.Celsius} C");
+    }
+}

languages/csharp/03-advanced/constructors-and-invariants/exercises/01.cs

@@ -0,0 +1,67 @@
+using System;
+
+class BankAccount
+{
+    private double balance;
+
+    public BankAccount(double initialBalance)
+    {
+        balance = initialBalance < 0.0 ? 0.0 : initialBalance;
+    }
+
+    public bool Deposit(double amount)
+    {
+        if (amount <= 0.0)
+        {
+            return false;
+        }
+
+        balance += amount;
+        return true;
+    }
+
+    public bool Withdraw(double amount)
+    {
+        if (amount <= 0.0 || amount > balance)
+        {
+            return false;
+        }
+
+        balance -= amount;
+        return true;
+    }
+
+    public double Balance => balance;
+}
+
+class Program
+{
+    static void Main()
+    {
+        Console.Write("Initial balance: ");
+        if (!double.TryParse(Console.ReadLine(), out double initialBalance))
+        {
+            Console.WriteLine("Invalid initial balance.");
+            return;
+        }
+
+        BankAccount account = new BankAccount(initialBalance);
+
+        Console.Write("Deposit amount: ");
+        if (double.TryParse(Console.ReadLine(), out double depositAmount))
+        {
+            account.Deposit(depositAmount);
+        }
+
+        Console.Write("Withdraw amount: ");
+        if (double.TryParse(Console.ReadLine(), out double withdrawAmount))
+        {
+            if (!account.Withdraw(withdrawAmount))
+            {
+                Console.WriteLine("Withdrawal rejected.");
+            }
+        }
+
+        Console.WriteLine($"Final balance: {account.Balance}");
+    }
+}

languages/csharp/03-advanced/constructors-and-invariants/exercises/02.cs

@@ -0,0 +1,45 @@
+using System;
+
+class SimpleDate
+{
+    private readonly int month;
+    private readonly int day;
+
+    public SimpleDate(int monthValue, int dayValue)
+    {
+        month = monthValue;
+        day = dayValue;
+    }
+
+    public bool IsValid()
+    {
+        if (month < 1 || month > 12)
+        {
+            return false;
+        }
+
+        int[] daysInMonth = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+        return day >= 1 && day <= daysInMonth[month - 1];
+    }
+}
+
+class Program
+{
+    static void Main()
+    {
+        Console.Write("Enter month and day: ");
+        string raw = Console.ReadLine() ?? string.Empty;
+        string[] parts = raw.Split(' ', StringSplitOptions.RemoveEmptyEntries);
+
+        if (parts.Length != 2 ||
+            !int.TryParse(parts[0], out int month) ||
+            !int.TryParse(parts[1], out int day))
+        {
+            Console.WriteLine("Invalid input.");
+            return;
+        }
+
+        SimpleDate date = new SimpleDate(month, day);
+        Console.WriteLine(date.IsValid() ? "Valid date" : "Invalid date");
+    }
+}

languages/csharp/CHECKLIST.md

@@ -23,6 +23,7 @@
 ## 03-advanced
 
 - [ ] Complete `03-advanced/structs-and-classes`.
+- [ ] Complete `03-advanced/constructors-and-invariants`.
 
 ## Parity Goals
 

languages/csharp/README.md

@@ -6,7 +6,7 @@ This track currently covers `01-foundations`, `02-core`, and early `03-advanced`
 
 - 8/8 foundations modules implemented.
 - 6/6 core modules implemented (`input-validation`, `algorithms-basics`, `file-io-basics`, `sorting-and-searching`, `maps-and-frequency-counting`, `error-handling-and-defensive-programming`).
-- 1/5 advanced modules implemented (`structs-and-classes`).
+- 2/5 advanced modules implemented (`structs-and-classes`, `constructors-and-invariants`).
 - Same module naming as C++, Python, and Go for parity.
 
 ## Prerequisites
@@ -47,6 +47,7 @@ dotnet run --project 01-foundations/types-and-io/example/types-and-io-example.cs
   - [error-handling-and-defensive-programming](./02-core/error-handling-and-defensive-programming/README.md)
 - [03-advanced](./03-advanced/README.md)
   - [structs-and-classes](./03-advanced/structs-and-classes/README.md)
+  - [constructors-and-invariants](./03-advanced/constructors-and-invariants/README.md)
 
 ## Progress Tracking