Linq in practice
•Download as PPTX, PDF•
1 like•485 views
Copy: https://docs.google.com/presentation/d/1JKNJDU6KTnzaebh1U2qWRJ6t_E9GNTXY9w-ywDpWRYQ/edit?usp=sharing
Recommended
Recommended
More Related Content
Similar to Linq in practice
Similar to Linq in practice (20)
More from Tuomas Hietanen
More from Tuomas Hietanen (14)
Recently uploaded
Recently uploaded (20)
Linq in practice
- 1. LINQ in practice ”In theory there is no difference between theory and practice. But in practice there is”. Except in mathematics…
- 2. Func<TIn1, TIn2, TOut> public int PlusFive(int i){ return i+5; } Func<int, int> PlusFive = delegate(int i) { return i + 5; }; Func<int, int> PlusFive = i => i + 5;
- 4. ” Infiniteloop” publicstaticIEnumerable<int> NaturalNumbers() { inti=0; while(true){ yieldreturn i++; } }
- 5. Filtered publicstaticIEnumerable<int> Odds() { returnNaturalNumbers().Where(i=>i%2==1); }
- 6. It works! static void Main(string[] args) { var nums = Odds().Take(5); //var executed = nums.ToList(); foreach(var i in nums) Console.WriteLine(i); }
- 7. What is inside LINQ? public static class FetchExtension{ public static IEnumerable<T> MyWhere<T>( this IEnumerable<T> list, Func<T, bool> cond){ foreach(var i in list){ if (cond(i)) yield return i; } } }
- 8. Imperative vs. declarative var result = new List<int>(); foreach(var i in list){ if(i % 2 == 0){ result.Add(i); } } var result = from i in list where i % 2 == 0 select i;
Editor's Notes
- Func<…> is “function as type”These code blocks are equals.First type parameters are input parameters. The last type parameter is the return valueIn type declaration we already know the function type…
- Instead of List<T> use the base classIEnumerable<T>- It is the base class for the lists (and LINQ) It doesn’t contain any kind of .RemoveAt(…) methods, so no-one will mess with your list
- Using System.LinqFilter the ones that are not interesting
- When you debug you notice what happens! Don’t do if(list.Count() == 0) but if(!list.Any()) so you don’t evaluate the whole list
- Declarative is better: Higher level of abstaction Define what computer does, not howSQL-like syntax is not the point, but the functionality!SQL-like syntax is just one way to express .Where(i=>i%2==0);