Code equivalent to the 'let' keyword in chained LINQ extension method calls

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Using the C# compilers query comprehension features, you can write code like:

var names = new string[] { "Dog", "Cat", "Giraffe", "Monkey", "Tortoise" };
var result =
    from animalName in names
    let nameLength = animalName.Length
    where nameLength > 3
    orderby nameLength
    select animalName;

In the query expression above, the let keyword allows a value to be passed forward to the where and orderby operations without duplicate calls to animalName.Length.

What is the equivalent set of LINQ extension method calls that achieves what the "let" keyword does here?

extension-methods linq-to-objects linq c#
4 Answers

Let doesn't have its own operation; it piggy-backs off of Select. You can see this if you use "reflector" to pull apart an existing dll.

it will be something like:

var result = names
        .Select(animalName => new { nameLength = animalName.Length, animalName})
        .Where(x=>x.nameLength > 3)
        .OrderBy(x=>x.nameLength)
        .Select(x=>x.animalName);
Marc_Gravell_233540

There's a good article here

Essentially let creates an anonymous tuple. It's equivalent to:

var result = names.Select(
  animal => new { animal = animal, nameLength = animal.Length })
.Where(x => x.nameLength > 3)
.OrderBy(y => y.nameLength)
.Select(z => z.animal);
Keltex_282600

about Code equivalent to the 'let' keyword in chained LINQ extension method calls

above comment is no more valid

var x = new List<int> { 2, 3, 4, 5, 6 }.AsQueryable();
(from val in x
let val1 = val
let val2 = val + 1
where val2 > val1
select val
).Dump();

produces 

System.Collections.Generic.List`1[System.Int32]
.Select(
  val =>
     new
     {
         val = val,
         val1 = val
     }
)
.Select(
  temp0 =>
     new
     {
         temp0 = temp0,
         val2 = (temp0.val + 1)
     }
)
.Where(temp1 => (temp1.val2 > temp1.temp0.val1))
.Select(temp1 => temp1.temp0.val)

so multiple let are optimized now

user_17166200
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