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type-exercise-in-rust
Learn Rust dark magics by implementing an expression framework in database systems
The problem is partially addressed using the combination of generics and declarative macros in the blog, as well as in the initial implementation of RisingWave.
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Then, utilize declarative macros to generate various types of kernel functions, including functions with 1, 2, and 3 parameters, as well as the input/output combinations of T and Option. Common kernels like unary, binary, ternary, unary_nullable and unary_bytes are generated, partially addressing the last two issues. (For the implementation details, see RisingWave's earlier code.) Theoretically, type exercise could also be used here. For example, introducing a trait to unify (A,), (A, B) and (A, B, C), or utilizing traits of Into and AsRef to unify T, Option, and Result, etc. However, you will probably encounter some type challenges posed by rustc.
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For this purpose, dtolnay from the Rust community has created two ready-to-use libraries: linkme and inventory. The former directly utilizes the above mechanism, while the latter uses the C standard constructor function, but the underlying principles are essentially the same. Let's take linkme as an example to demonstrate how to implement the registration mechanism.
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For this purpose, dtolnay from the Rust community has created two ready-to-use libraries: linkme and inventory. The former directly utilizes the above mechanism, while the latter uses the C standard constructor function, but the underlying principles are essentially the same. Let's take linkme as an example to demonstrate how to implement the registration mechanism.
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By the way, genawaiter is also an interesting library that uses the async-await mechanism to implement the generator in the stable version of Rust. As we know, async-await is essentially a generator, and also relies on the compiler’s CPS transformation to implement the state machine. However, async-await was stabilized a long time ago due to the strong need for asynchronous programming, whereas the generator feature lagged behind. The similar principles behind them allows their mutual implementation. In addition, the Rust community is actively promoting async generators, with native async gen and for await syntax entering the nightly version. However, since it is not integrated with the futures ecosystem, it remains in an unusable state overall. RisingWave‘s stream processing engine relies heavily on async generator ****mechanism to implement its streaming operators, simplifying streaming state management under asynchronous IO. That's another extensive topic, and we'll discuss the relevant applications if there is an opportunity later.
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The #[function] macro is originally developed as a framework for internal function implementation in RisingWave. Recently, we extract it from RisingWave projects and standardizes it into a set of general user-defined function interfaces arrow-udf based on Apache Arrow. If your project also uses arrow-rs for data processing, you can now define your own functions directly using this set of #[function] macros. If you're using RisingWave, then starting with version 1.7, you can use this library to define Rust UDFs. It can be compiled into a WebAssembly module and inserted into RisingWave for execution. If interested, you can read the source code of this project for more implementation details.
