Using LINQ on the client-side

WebSharper provides support to process IEnumerable sequences using LINQ queries on the client side.

Simple queries

You can use LINQ query syntax in client-side code like you would in .NET.

using System;
using System.Linq;
using System.Collections.Generic;
using WebSharper;
 
namespace TestLinq
{
    [JavaScript]
    public class App
    {
        public static void Main()
        {
            var people = new[] { "Don", "Simon", "Rich", "Joe", "Martin" };
 
            var oddPeople =
                from person in people
                where person.Length % 2 == 1
                orderby person.Length
                select person;
 
            Console.Log("People whose names have an odd length:");
            foreach (var person in oddPeople)
            {
                Console.Log("  " + person);
            }
            // prints:
            // People whose names have an odd length:
            //   Don
            //   Simon
            //   Joe
        }
    }
}

Of course, you can use explicit LINQ extension methods if you prefer.

public static void Main()
{
    var people = new[] { "Don", "Simon", "Rich", "Joe", "Martin" };
 
    var oddPeople = people
        .Where(person => person.Length % 2 == 1)
        .OrderBy(person => person.Length);
 
    Console.Log("People whose names have an odd length:");
    foreach (var person in oddPeople)
    {
        Console.Log("  " + person);
    }
    // prints:
    // People whose names have an odd length:
    //   Don
    //   Simon
    //   Joe
}

Other Linq methods

WebSharper provides proxies for all IEnumerable extension methods from System.Linq, such as .Concat(), .ToArray() or .ElementAt():

public static void Main()
{
    var people = new[] { "Don", "Simon", "Rich", "Joe", "Martin" };
    var morePeople = people.Concat(new[] { "Xavier", "Evan" }).ToArray();
 
    Console.Log("The sixth person is", morePeople.ElementAt(5));
    // prints:
    // The sixth person is Xavier
}

Using custom comparers

Advanced uses of Linq methods are possible, such as custom comparers. Here is an example where we make a sequence's items distinct by their length using an EqualityComparer:

public static void Main()
{
    var people = new[] { "Don", "Simon", "Rich", "Joe", "Martin" };
 
    var distinctPeople = people.Distinct(new ByLength());
 
    foreach (var person in distinctPeople)
    {
        Console.Log(person);
    }
    // prints:
    //   Don
    //   Simon
    //   Rich
    //   Martin
}
 
public class ByLength : EqualityComparer<string>
{
    override public bool Equals(string x, string y)
    {
        return x.Length == y.Length;
    }
 
    public override int GetHashCode(string x)
    {
        return x.Length;
    }
}

Methods dealing with default values

Some Linq methods use the default value of the element type. For example, .FirstOrDefault() returns the first element of the IEnumerable, or a default type if it is empty. This default value depends on the type: for example, if the element type is int, then the default value is 0, whereas if the element type is a class, then the default value is null. WebSharper can provide the correct default value, on the condition that the element type is known statically. For example, the following will run correctly:

public static void Main()
{
    var people = new string[] { };
    var onePerson = people.FirstOrDefault();
    Console.Log(onePerson);
    // prints:
    // null
}

However, the following will fail to compile because the element type is not known statically:

public static T GetDefaultPerson<T>(IEnumerable<T> people)
{
    return people.FirstOrDefault();
    // compile error:
    // Macro 'WebSharper.MacroModule+DefaultOf' requires a resolved type argument.
}

In this case, you can add the [Inline] attribute to the method to make its content to be inserted at every call point, with all code generation needing known types to be resolved appropriately.

Using LINQ on the client-side

Simple queries

Other Linq methods

Using custom comparers

Methods dealing with default values

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