Types are the universal abstraction that enables CLI-based programs to interact with the operating system, with foreign code, and with the world of the microprocessor. Below the CLI lurks a world of address spaces, threads, instructions, interrupts, and registers, defined by the operating system and microprocessor being used. Above the CLI, high-level programming languages project component-based abstractions that help to ease programmer interactions with those painfully concrete low-level constructs. Types are the organizational principle that bridges these two worlds safely, efficiently, and consistently. To understand how the CLI creates native code and maintains control over its execution, it is first important to understand its
The notion of a type system can be difficult to define. For most programmers, the old adage, “I can’t tell you what it is, but I know it when I see it” describes their definition of a type system. Intuitively, we know that primitive types, classes, structs, and such are part of a type system, and that languages will enforce certain rules regarding the use of these types. But to actually say, in formal terms, what a type system is and entails is difficult. Nonetheless, most programmers, regardless of their background, will be able to infer some interesting details about the CLI type system from Example 3-1, even if they’re not familiar or comfortable with C#.
Example 3-1. The ...