{"id":"language--contracts","name":"Requires, ensures, and invariants","owner":"yeho","package":"language","kind":"language","signature":"Function(...) -> Type requires(condition) ensures(condition) { ... }\ninvariant(condition)","description":"Contracts attach executable meaning to valid inputs, promised outputs, and valid object state.","context":"Use contracts at important boundaries where callers and maintainers need one visible definition of correctness.","parameters":[],"returns":"","members":[],"tags":["complete-program","cpu","ensures","functions","invariant","language","requires","yeho"],"updated":"2026-09-09","source":{"repository":"yeho","path":"parser_declarations.cpp parseContractClauses and parseThingInvariant; conformance errors-contracts"},"status":"experimental","notes":["Errors and contracts are experimental in the current conformance edition.","Keep the condition deterministic and cheap enough to be useful as evidence."],"examples":[{"id":"complete","title":"Contract pass","description":"Use contracts at important boundaries where callers and maintainers need one visible definition of correctness.","code":"Increment(int value) returns int\nrequires(value > 0)\nensures(result == value + 1)\n{\n    return value + 1\n}\n\nConsole.Log(Text.From(Increment(4)))\n","manifest":"package = \"tests.compiler.errorsTasksEffects.contractPass\"\nversion = \"0.1.0\"\nbackend = \"cpu-oracle\"\nosTarget = \"windows\"\narchTarget = \"x64\"\nselfContainedApp = false\n","tags":["cpu","complete-program"],"verification":"type checked","run":"cpu-oracle","source":"tests/compiler/errors-tasks-effects/contract-pass/start.yh","sha256":"7596733f355e82045916ad1e562cd4626d8883b61d0d8037ca088e9300e1733e","checked":"2026-09-09","diagnostic":"","observedOutput":null,"checkedBackend":null}],"searchTerms":[],"url":"https://demonhunterlabs.com/academy/api?item=language--contracts","json":"https://demonhunterlabs.com/reference/items/language--contracts.json","markdown":"https://demonhunterlabs.com/reference/text/language--contracts.md"}