How C# Compiles yield return Into a State Machine

Short summary

The article explains how C#'s yield return is implemented by the compiler as a hidden state machine class, not as magical method pausing. Local variables are promoted to heap fields, execution is deferred until enumeration, and each yield becomes a new state. Understanding these mechanics clarifies debugging surprises and helps developers decide when lazy evaluation is an optimization versus a source of complexity.

• •yield return compiles into a hidden iterator class with a state machine
• •Local variables become heap fields; execution is deferred until enumeration
• •One allocation replaces another—useful for memory-constant large reads but not always the right tool

Generated with AI, which can make mistakes.