Static preconditions

[mark-i-m]

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Idea: Static assertions

Idea (Apologies in advance for the hand-wavy-ness) Introduce the compile-time assertions based on supported const eval. For example, const BUF_SIZE: usize = 500; const MAX_BUF_SIZE: usize = 1000; static_assert(BUF_SIZE <= MAX_BUF_SIZE) // static assert static_assert(10000000 < MAX_BUF_SIZE) // compile error: assertion failed... Inside the static_assert can be any const expression of type bool that is accepted by the compiler. Motivation Often, it can be helpful to assert the truthiness of …

Compile time assert

Yes, I know about this trick, there is also static_assertions crate that provides nice wrapper around this or similar trick. But it would be great to have it inside std or compiler.

Quick Thought: const{} blocks

Looking at async fn+async{} and unsafe fn+unsafe{} made me think, what about const{}? As an example, (function-level) static_assert!(N == M) could just be const { assert_eq!(N, M) } (Ref Idea: Static assertions & RFC #2345 Allow panicking in constants) I could also imagine something like match x { 0..N => ..., N..const{2*N} => ..., _ => ... }. You could think of this as const { A } => (const || { A })(), like with async – not that const closures exist today.