LINQ Interview Question #76

What does deferred execution mean in LINQ?

Deferred Execution, Immediate Execution & Query Behavior Mid-Level Intermediate

Quick Interview Answer

Deferred execution means that defining a LINQ query does not necessarily execute it immediately. Many sequence-returning operators, including Where and Select, store the query logic and perform the work when the result is enumerated.

Detailed Explanation

This allows queries to be composed before execution. It also means the data observed by a query can change between query definition and enumeration.

Code Example

var query = numbers.Where(n => n > 10);

// No enumeration yet.
foreach (var number in query)
{
    Console.WriteLine(number);
}