unmanaged, notnull, new() (C# 6 emulation)
C# 6 supports class/struct/new() constraints; emulate newer notnull/unmanaged via guards, API shape, and conventions.
unmanaged, notnull, new() (C# 6 emulation) is a free C# Academy lesson on CoddyKit — lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Constraints landscape
Goal: Use C# 6 generic constraints effectively.
- class vs struct
- new() for activator-less creation
- Emulate notnull/unmanaged with guards and API design
class vs struct
class confines T to reference types; struct confines T to value types. Misuse fails at compile time.
using System;
// Works only for reference types
public static class RefBox
{
public static string Show<T>(T value) where T : class
{
return value == null ? "null ref" : "ref: " + value.ToString();
}
}
// Works only for value types
public static class ValBox
{
public static string Show<T>(T value) where T : struct
{
return "value: " + value.ToString();
}
}
public class Program
{
public static void Main(string[] args)
{
string s = "hello";
int n = 42;
Console.WriteLine(RefBox.Show<string>(s)); // OK
Console.WriteLine(ValBox.Show<int>(n)); // OK
// Console.WriteLine(RefBox.Show<int>(n)); // compile-time error (int is struct)
// Console.WriteLine(ValBox.Show<string>(s)); // compile-time error (string is class)
}
}
new() in practice
new() guarantees a public parameterless constructor so generic code can call new T() directly.
using System;
// Requires public parameterless ctor on T
public static class Factory
{
public static T Create<T>() where T : new()
{
return new T(); // safe in C# 6 with new()
}
}
public sealed class Sample
{
public string Name { get; set; }
public Sample() { Name = "default"; }
}
public class Program
{
public static void Main(string[] args)
{
Sample x = Factory.Create<Sample>();
Console.WriteLine("Created: " + x.Name);
}
}
Emulate notnull
No notnull in C# 6. Approximate by where T : class plus explicit null guards inside the API.
using System;
// C# 6 has no notnull constraint. Use where T : class and guard at runtime.
public static class NotNullApi
{
public static int LengthOf<T>(T x) where T : class
{
if (x == null) throw new ArgumentNullException("x");
return x.ToString().Length; // placeholder usage
}
}
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine(NotNullApi.LengthOf<string>("hi")); // 2
try
{
Console.WriteLine(NotNullApi.LengthOf<string>(null)); // throws
}
catch (Exception ex)
{
Console.WriteLine("Guard fired: " + ex.GetType().Name);
}
}
}
Emulate unmanaged intent
No unmanaged in C# 6. You can use struct and interfaces (e.g., IComparable) to target numeric-like value types.
using System;
// No unmanaged constraint in C# 6.
// Use struct for value types and restrict API usage (document numeric-only intent).
public static class NumericOps
{
public static T Max<T>(T a, T b) where T : struct, IComparable
{
// Works for numeric primitives because they implement IComparable
return (a.CompareTo(b) >= 0) ? a : b;
}
}
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine(NumericOps.Max<int>(3, 9)); // 9
Console.WriteLine(NumericOps.Max<double>(2.5, 2)); // 2.5
}
}
Practical tips
Tips:
- Pick class/struct to narrow T early.
- Use new() if you need to create T.
- Emulate notnull with runtime guards.
- Emulate unmanaged via struct + documented usage (often numeric primitives).
Constructor constraint
Recap
Recap: Use class/struct/new() in C# 6. Emulate notnull with null checks and unmanaged intent with struct + interface bounds.
Frequently asked questions
Is the “unmanaged, notnull, new() (C# 6 emulation)” lesson free?
Yes — the full text of “unmanaged, notnull, new() (C# 6 emulation)” is free to read here on the web, and the C# Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO.
What will I learn in “unmanaged, notnull, new() (C# 6 emulation)”?
C# 6 supports class/struct/new() constraints; emulate newer notnull/unmanaged via guards, API shape, and conventions. You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start C# Academy?
No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “unmanaged, notnull, new() (C# 6 emulation)” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this C# Academy lesson?
Yes. Every C# Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- unmanaged, notnull, new() (C# 6 emulation)
- Generic math (overview), generic attributes (when relevant)
- Reusable generic utilities