![]() ![]() Or, we might get lazy and not check them at all, instead In most other languages, we would have to handle these with runtime checks andĮrrors/exceptions. “Once you have done action A, you must perform either B or C (but not both) Succeeded, and not after we have ended the session.” “These messages can only be sent to the client after authentication has “You must not perform any I/O operations on a file handle after it’s been “The buffer can only be translated if you have checked that it’s valid UTF-8.” I don’t have implementations of all of them): Of properties that can be enforced by the typestate pattern in Rust (I assert The special case of typestates that interests us here is the way they canĮnforce run-time order of operations at compile-time. Which is why I’m calling it the “typestate pattern.” Typestates are a broader topic than the specific pattern I’ll discuss here, That the compiler can check ahead-of-time). Information a program is processing) into the type level (the static world ![]() Typestates are a technique for moving properties of state (the dynamic I haven’t seen a detailed examination of the nuances of this pattern, so here’s Languages - most of them fail to satisfy items number 2 and/or 3 above. Interestingly, it’s very difficult to implement in most other programming You may have already written code that uses it, perhaps without realizing it. This pattern is so easy in Rust that it’s almost obvious, to the point that It can eliminate run-time checks, making code faster/smaller.It interacts nicely with IDEs, which can avoid suggesting operations that are.It moves certain types of errors from run-time to compile-time, giving.Type-level state of objects in addition to, or instead of, changing run-timeĭynamic state, such that the operations in the previous state are no longer State transition operations (methods or functions) that change the The operations in the wrong state fail to compile, Operations on an object (such as methods or functions) that are only availableĪ way of encoding these states at the type level, such that attempts to use The typestate pattern is an API design pattern that encodes information aboutĪn object’s run-time state in its compile-time type. Variation: state types that contain actual state. ![]()
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