C# & .NET Language Essentials

Value and reference behavior, structs, boxing, generics, delegates, LINQ execution, nullability, exceptions, reflection, closures, iterators, collections, pattern matching, and extension methods.

12 drillsPractice one at a timeOrdered pathConcept questionDebugging scenarioComparison questionArchitecture scenario

Recommended start

Value and reference semantics

Explains what is copied when values and object references are assigned or passed, including the explicit effect of ref, out, and in.

Easy~5 minStep 1 of 12

Practice this drill Choose another

1Value and reference semanticsRecommended startExplains what is copied when values and object references are assigned or passed, including the explicit effect of ref, out, and in.Concept questionEasy~5 min.NETC#Practice 2Mutable structs and copiesDiagnoses lost struct mutations and explains how readonly access can trigger defensive copies.Debugging scenarioMedium~10 min.NETC#Practice 3Boxing and structsExplains when a value is wrapped as an object, why unboxing is exact, and how generic APIs can avoid hidden allocations.Concept questionMedium~7 min.NETC#Practice 4Generic constraints and varianceUses constraints to express required operations and explains safe assignment direction for generic producers and consumers.Comparison questionHard~9 min.NETC#Practice 5Delegates and eventsDistinguishes callable delegate values from publisher-controlled events and makes subscription lifetime explicit.Comparison questionMedium~7 min.NETC#Practice 6Nullable reference boundariesUses nullable annotations as a compile-time contract while still validating untrusted and legacy runtime inputs.Architecture scenarioMedium~10 min.NETC#Practice 7Exception handling boundariesPreserves failure context, catches only where recovery or translation is possible, and uses filters without hiding unrelated faults.Architecture scenarioHard~12 min.NETC#Practice 8Reflection and AOTUses metadata-driven behavior deliberately and protects reflection-dependent code when publishing with trimming or ahead-of-time compilation.Architecture scenarioHard~12 min.NETC#Practice 9Closures and captured stateExplains what a lambda captures, how captured state is shared, and why a long-lived callback can retain more memory than expected.Debugging scenarioMedium~10 min.NETC#Practice 10Time modeling in .NETDistinguishes instants, local calendar values, offsets, and named time zones so APIs and persistence survive daylight-saving and locale boundaries.Comparison questionMedium~7 min.NETC#SQL ServerPractice 11Pattern matching decisionsUses type, property, relational, and list patterns to express decisions while keeping null and unhandled cases explicit.Architecture scenarioMedium~10 min.NETC#Practice 12Extension method resolutionExplains static extension binding, instance-member precedence, namespace ambiguity, null receivers, and compatibility when APIs evolve.Concept questionHard~9 min.NETC#Practice