C# Evolved

LINQ

C# 3.0 NETFx 3.5

Published Updated Author Jeffrey T. Fritz Reading time —

LINQ gives C# a consistent way to filter, transform, group, and sort data with either query syntax or fluent method syntax.

LINQ was introduced in C# 3.0. It combines language features and framework extensions so you can express data queries directly in C#.

Why it matters

LINQ matters because it replaces hand-written iteration with intent-focused operators. You can read the shape of the data transformation from left to right instead of tracing index updates and accumulator variables.

It also works across different backends. In-memory collections, XML, and many data providers can all use the same query style.

Cautions

Not every loop should become LINQ. If the code relies on side effects, early exits, or complex branching, a simple foreach can be clearer.

Also remember that deferred execution can delay work until enumeration time, which is useful but easy to forget when debugging.

Filtering and projecting data

LINQ turns sequence processing into a readable pipeline instead of nested loops and temp variables.

Valid since C# 3.0 

var people = new[]
{
    new { Age = 30, LastName = "Smith", FullName = "Alice Smith" },
    new { Age = 16, LastName = "Jones", FullName = "Bob Jones" },
    new { Age = 25, LastName = "Brown", FullName = "Carol Brown" },
};

var adults = people
    .Where(person => person.Age >= 18)
    .OrderBy(person => person.LastName)
    .Select(person => person.FullName);

Extension methods

C# 3.0 NETFx 3.5

Start with Extension methods when you want an earlier building block for LINQ.

Extension methods let you add discoverable helpers to existing types, which is why they show up everywhere from LINQ to application-specific fluent APIs.

Local functions

C# 7.0 NETFx 4.7

Continue to Local functions for the next guide in this theme.

Local functions are methods defined inside other methods or properties, letting you encapsulate helper logic at the point of use. They reduce namespace clutter, improve readability by keeping related logic together, and naturally capture variables from their enclosing scope.

Lambda expressions

C# 3.0 NETFx 3.5

Explore Lambda expressions for another earlier stepping stone in the same theme.

Lambda expressions make delegate-based code shorter and easier to scan, especially when you pass behavior into LINQ, events, and async APIs.

Default Interface Members

C# 8.0 NETCore 3.0

Explore Default Interface Members to take the same theme one step further.

Evolve interfaces by adding members with default implementations so existing implementers do not break immediately.

Learn more

LINQ (Microsoft Learn)