[noblethrasher]

We've had a robust way of doing code contracts since C# 2.0.

If you instruct the compiler to treat all warnings as errors (so that variables must be defintitely assigned), then the following code gives you what you want:

	 public PositiveInt SomeMethod(GreaterThanFive a, NonNegative b)
	 {
	 		//do stuff;
	 } 
     
	 public struct GreaterThanFive
	 {
	 	readonly int n;
	 	
	 	public GreaterThanFive (int n)
	 	{
	 		if(n < 5)
				throw new ArgumentException("n must be greater than 5")
			
			this.n = n;
	 	}
	 	
	 	public static implicit operator GreaterThanFive(int n)
	 	{
	 		return GreaterThanFive(n);
	 	}
	 	
	 	public static implicit operator int (GreaterThanFive n)
	 	{
	 		return n.n;
	 	}
	 }

	//Similar definitions for NonNegative and PositiveInt

We can even have nice diagnostic messages since the advent of C# 5's CallerInfo attributes (CallerMemberName, CallerLineNumber, and CallerFilePath).

[MichaelGG]

Very clever. It may be robust, but is ridiculously verbose and feels sorta obfuscatory. Also pays a runtime penalty unless they've improved the CLR codegen.

It also might not be super amenable to static analysis.

[noblethrasher]

But, structs pay a very small runtime penalty, if at all, right?

The verbosity will be mostly ameliorated with primary constructor. I propose going further by allowing programmers to annotate constructors so that they can be used as user-defined conversion operators.

Thus, the aforementioned code could become something like:

	 public struct GreaterThanFive implicit (int n)
	 {
	 	readonly int n = n;

	 	if(n <= 5)
	 	    throw new ArgumentException("n must be greater than 5");	 	

	 }

[MichaelGG]

Traditionally, structs paid a large codegen penalty, as a lot of optimizations and stuff were turned off. It also seemed like the codegen wasn't super smart about passing them around. Maybe that's all changed.

I meant the verbosity of having to create a custom type for each kind of restriction, versus some inline "int n [n > 5]" notation.

[noblethrasher]

In addition to the benefit of brevity, something like your proposal also has the virtue of being compatible with the `checked/unchecked` keywords.