Day 02 Generics Deferred enumerables and LINQ

Day 02 - Generics, Deferred Enumerables and LINQ

Projects:

Fun With Generics	Touching the hard points of .net Generics: Constraints, Covariance and Inference
Intro to LINQ	Introduction to the lazy nature of .net LINQ

Generics

• The purpose of Generics
• About Boxing and Unboxing
• Static members of Generic classes
• Generic Inference
• Generic Invariance, Covariance and Contravariance
• Generic Constraints

Equatable Value type

• We have created a value type for complex numbers: Complex
• We have implemeneted IEquatable<Complex> to allow it to compare itself to other Complex instances
• We discussed the Equals that we derive from object and how to override it
• We talked about how to overload the == operator
  • Always implement the != operator too (the compiler enforces it)
  • Always override the Equals method from object (the compiler warns if you do not)
  • Always override the GetHashCode method too (the compiler warns if you do not) - this is important to allow the object to be used as key in HashSets

Intro to deferred execution in LINQ

• We have created an iterator method using yield return
• We have investigated the deferred execution nature of the enumerable and spotted 3 significant points in time:
  • Calling the method itself - creates an instance of the IEnumerable
  • Starting the foreach - creates an instance of the IEnumerator
  • Fetching the next item - runs the iterator method until the next yield return
• We discussed the 2 ways to terminate an iterator
  • By ending the method
  • By calling yield break
• We Defined an IEnumerable Operator as
  • A function that has predictable output per input
  • That does not cause side effects
  • That creates a new IEnumerable out of its source enumerable
• We created a Map operator that accepts a generic delegate and projects a new enumerable out of the source by applying the projection delegate on each item
• We created a TakeFirst operator that accepts a (possibly) infinite stream and completes after the first few items
• We discussed how infinite enumerables are even possible in the deferred execution paradigm
• Finally we talked about the basic most common LINQ operators:
  • Select projection operator
  • Where filtering operator
  • OrderBy and ThenBy sorting operators
  • Zip combining operator

TBC next week