Compile-time optimized bounds checking of user-defined types is provided. A user-defined class has an annotated memory-accessing method, and an annotated bound-providing member such as an integer field containing a bound or a method that returns a bound when called. The user-defined-bounds check may supply bounds checking where the programming language has none, or it may supplement existing bounds checks, e.g., by wrapping a built-in array type or a garbage-collector-managed type. Bounds checking can be extended beyond arrays and other types whose layout is controlled by a compiler, allowing efficient systems programming in a managed code environment. A bounds-check representation is inserted by the compiler in intermediate language code. Optimization then reduces duplicative bounds checking.