Rust Contracts syntax

[codeOverFlow]

Hello, maybe a newbie question, but why use attributes instead of language syntax similar to where clause, and similar to what Ada does ?

[fmease]

Without speaking for the parties involved in designing and implementing this feature, #![feature(contracts)] is a highly experimental feature that's not backed by an RFC (yet). The syntax is likely temporary. CC this paragraph from compiler MCP 759:

My example above has leveraged an attribute-based surface syntax. It is possible that we will find that other non-attribute construct are more appropriate for some situations. (For example, I have seen suggestions that type invariants would be better off framed as an instance of a trait that a type implements.)

See also

• MCP: Contracts: Experimental attributes and language intrinsics compiler-team#759
• Lang experiment approval: #[contracts::requires(...)] + #[contracts::ensures(...)] #128045 (comment)
• Tracking issue: Tracking Issue for Contracts #128044