Guided course · C# Language

C# Internals: Value Types, Reference Types and the Heap

How value types and reference types really work: the stack-versus-heap truth, a precise storage model, boxing, the large-struct trap and a framework for choosing between struct and class, with a quiz, a coding exercise and a benchmark. This is not a memorization handout. It is a guided model-building exercise. Read one section, run the code, redraw the memory picture from memory, and then explain the result aloud. If your explanation uses the words “it just does that,” the model is not yet complete. Recommended learning loop: Predict first. Before reading an output or diagram, write what you expect. Trace the bits. Ask: what exact value is copied, and where is the destination storage? Inspect lower layers. Compare C# semantics, representative IL, and likely JIT behavior. Measure. Use BenchmarkDotNet only after you can state a hypothesis. Teach it back. Explain the concept without saying “structs are on the stack.” Scope boundary: This course deliberately masters one foundation: value semantics versus reference semantics, and how those semantics relate to storage. Boxing, ref/in/out, ref struct, string interning, and advanced GC behavior are introduced only where they clarify this model. Boxing and ref/in/out have their own courses. Mastery gate: Do not continue past this course until you can answer all four questions without guessing: What does a variable of a value type contain? What does a variable of a reference type contain? Why can a struct live inside a heap object? Why is a reference-type parameter still passed by value unless marked ref, in, or out? Lesson thesis: Type category answers a semantic question. Storage location answers a placement question. They are related, but they are not the same question.