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How do you implement the 'checked' operator overload variant (introduced in C# 11) to provide overflow-checking behavior for a custom numeric type?

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Answer

C# 11 lets you define a SEPARATE overload of an operator specifically for 'checked' contexts (using 'checked operator +' syntax) alongside the normal unchecked version — the compiler automatically calls the checked variant when the surrounding code is in a 'checked' block/expression, letting custom numeric types participate correctly in C#'s overflow-checking semantics.
public struct SafeInt {
  public int Value;
  public static SafeInt operator +(SafeInt a, SafeInt b) => new SafeInt { Value = a.Value + b.Value }; // unchecked
  public static SafeInt operator checked +(SafeInt a, SafeInt b) =>
    new SafeInt { Value = checked(a.Value + b.Value) }; // throws OverflowException if it overflows
}
Real-world example Building a custom numeric type that correctly respects C#'s checked/unchecked overflow-detection context, matching built-in numeric type behavior.

Common follow-ups: In what scenario would the compiler automatically choose the checked overload over the regular one?

Exception Handling
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