Advantages/Disadvantages of different implementations for Comparing Objects

Question

This questions involves 2 different implementations of essentially the same code.

First, using delegate to create a Comparison method that can be used as a parameter whe

Answer 1

They really address different needs:

IComparable is useful for objects that are ordered. Real numbers should be comparable, but complex numbers cannot - it is ill-defined.

IComparer allows to define re-usable, well-encapsulated comparers. This is especially useful if the comparison needs to know some additional information. For example, you might want to compare dates and times from different time zones. That can be complicated, and a separate comparer should be used for this purpose.

A comparison method is made for simple comparison operations that are not complicated enough for reusability to be of any concern, e.g. sorting a list of customers by their first name. This is simple operation, hence does not need additional data. Likewise, this is not inherent to the object, because the objects are not naturally ordered in any way.

Lastly, there is IEquatable, which might be important if your Equals method can only decide if two objects are equal or not, but if there is no notion of 'larger' and 'smaller', e.g. complex numbers, or vectors in space.