Add support for comparisons

[mediocresurgeon]

Adds the following methods: Argument.GreaterThan() Argument.GreaterThanOrEqualTo() Argument.LessThan() Argument.LessThanOrEqualTo()

[ashmind]

The technical work looks great, but I wonder if use cases (not already covered by Positive and similar checks) are common enough. What are some use cases you have in mind for this one?

[mediocresurgeon]

The technical work looks great, but I wonder if use cases (not already covered by Positive and similar checks) are common enough. What are some use cases you have in mind for this one?

One real-world example might be String.Substring(int, int).

With the new functionality, we would be able to express the boundary conditions like so:

public string Substring (int startIndex, int length)
{
    Argument.PositiveOrZero(nameof(startIndex), startIndex); // or Argument.GreaterThanOrEqualTo(nameof(startIndex), startIndex, 0);
    Argument.LessThan(nameof(startIndex), startIndex, this.Length);
    
    Argument.PositiveOrZero(nameof(length), length); // or Argument.GreaterThanOrEqualTo(nameof(length), length, 0);
    Argument.LessThanOrEqualTo(nameof(length), length, this.Length - startIndex);
    
    // Implementation
}

[ashmind]

Thanks! Yep I was thinking of something like that or Array.CopyTo and similar. But feels like there are not that many of those?

Also just remember one other thought I had when I considered similar methods for v1: I feel in those specific examples general Less/Greater might not give a clear enough error.

E.g Argument.LessThan(nameof(startIndex), startIndex, this.Length); will tell you "Value cannot be greater than or equal to 10", which does explain why exactly, or what 10 is. What would be good instead is a custom exception message, e.g. "Start index cannot exceed string length (10)".

Similarly, instead of Argument.LessThanOrEqualTo(nameof(length), length, this.Length - startIndex); we might consider something like "Substring of length 10 starting at index 5 ends at index 15, which is located beyond the end of the string (10)" (that might be too verbose, first wording I could think of).

You could argue the same point about e.g. Positive... methods. But I feel 0 is kind of special -- e.g. for length getting "Value must be positive" seems more clear on its own than "Value must be less than 17" (what's 17?).

[mediocresurgeon]

You're right--the proposed exception message might be adequate for constants, but it doesn't meaningfully communicate how to untangle a more dynamic situation (eg "startIndex plus length indicates a position not within this instance").

How would you feel about including an overload for these new methods which allows the exception message to be specified?