.NET and C# interview questions

Gen 0 is nursery for short-lived objects

Span is a stack-only view over contiguous memory so I can slice arrays and strings without extra allocations.

ConfigureAwait false skips capturing the SynchronizationContext, which avoids deadlocks in libraries that wait on Tasks.

I keep the context short-lived, batch SaveChanges, disable tracking for reads, and consider ExecuteUpdate for bulk.

Not in source or appsettings committed to git.

I start with traces and a profiler, not guesses.

GC reclaims managed objects no longer referenced.

The built-in container registers services with lifetimes: transient, scoped, singleton.

EF Core is an ORM that maps C# classes to tables and generates SQL.

You need GetAwaiter returning something with IsCompleted, OnCompleted, and GetResult.

ref struct types like Span can only live on the stack so they can safely point at stack memory.

I never block on .Result or .Wait in ASP.NET request threads.

Expand then contract: add nullable columns, dual-write, backfill, switch reads, drop later.

SaveChanges and command interceptors add auditing, multi-tenant filters, or soft-delete stamps.

Clients send an Idempotency-Key

Authenticate during the handshake, authorize per message when needed, and validate origin.

Sensitive actions re-check recent MFA or password confirmation.

Prefer System.Text.Json source generation, reuse buffers, and avoid ToList on huge graphs.

Domain has no infra references

I use a hosted service with the processor SDK, complete on success, and abandon or dead-letter on failure.