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Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0726.md')
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diff --git a/compiler/rustc_error_codes/src/error_codes/E0726.md b/compiler/rustc_error_codes/src/error_codes/E0726.md new file mode 100644 index 000000000..e3794327f --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0726.md @@ -0,0 +1,46 @@ +An argument lifetime was elided in an async function. + +Erroneous code example: + +When a struct or a type is bound/declared with a lifetime it is important for +the Rust compiler to know, on usage, the lifespan of the type. When the +lifetime is not explicitly mentioned and the Rust Compiler cannot determine +the lifetime of your type, the following error occurs. + +```compile_fail,E0726 +use futures::executor::block_on; +struct Content<'a> { + title: &'a str, + body: &'a str, +} +async fn create(content: Content) { // error: implicit elided + // lifetime not allowed here + println!("title: {}", content.title); + println!("body: {}", content.body); +} +let content = Content { title: "Rust", body: "is great!" }; +let future = create(content); +block_on(future); +``` + +Specify desired lifetime of parameter `content` or indicate the anonymous +lifetime like `content: Content<'_>`. The anonymous lifetime tells the Rust +compiler that `content` is only needed until create function is done with +it's execution. + +The `implicit elision` meaning the omission of suggested lifetime that is +`pub async fn create<'a>(content: Content<'a>) {}` is not allowed here as +lifetime of the `content` can differ from current context: + +```ignore (needs futures dependency) +async fn create(content: Content<'_>) { // ok! + println!("title: {}", content.title); + println!("body: {}", content.body); +} +``` + +Know more about lifetime elision in this [chapter][lifetime-elision] and a +chapter on lifetimes can be found [here][lifetimes]. + +[lifetime-elision]: https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html#lifetime-elision +[lifetimes]: https://doc.rust-lang.org/rust-by-example/scope/lifetime.html |