From 20431706a863f92cb37dc512fef6e48d192aaf2c Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:11:38 +0200 Subject: Merging upstream version 1.66.0+dfsg1. Signed-off-by: Daniel Baumann --- src/doc/book/nostarch/appendix_a.md | 142 ++++++++++++++++++++++++++++++++++++ 1 file changed, 142 insertions(+) create mode 100644 src/doc/book/nostarch/appendix_a.md (limited to 'src/doc/book/nostarch/appendix_a.md') diff --git a/src/doc/book/nostarch/appendix_a.md b/src/doc/book/nostarch/appendix_a.md new file mode 100644 index 000000000..ca3883be4 --- /dev/null +++ b/src/doc/book/nostarch/appendix_a.md @@ -0,0 +1,142 @@ + + +[TOC] + +## Appendix A: Keywords + +The following lists contain keywords that are reserved for current or future +use by the Rust language. As such, they cannot be used as identifiers (except +as raw identifiers, as we’ll discuss in “Raw Identifiers” on page XX). +*Identifiers* are names of functions, variables, parameters, struct fields, +modules, crates, constants, macros, static values, attributes, types, traits, +or lifetimes. + +## Keywords Currently in Use + +The following is a list of keywords currently in use, with their functionality +described. + +* **`as` **: perform primitive casting, disambiguate the specific trait +containing an item, or rename items in `use` statements +* **`async` **: return a `Future` instead of blocking the current thread +* **`await` **: suspend execution until the result of a `Future` is ready +* **`break` **: exit a loop immediately +* **`const` **: define constant items or constant raw pointers +* **`continue` **: continue to the next loop iteration +* **`crate` **: in a module path, refers to the crate root +* **`dyn` **: dynamic dispatch to a trait object +* **`else` **: fallback for `if` and `if let` control flow constructs +* **`enum` **: define an enumeration +* **`extern` **: link an external function or variable +* **`false` **: Boolean false literal +* **`fn` **: define a function or the function pointer type +* **`for` **: loop over items from an iterator, implement a trait, or specify a +higher-ranked lifetime +* **`if` **: branch based on the result of a conditional expression +* **`impl` **: implement inherent or trait functionality +* **`in` **: part of `for` loop syntax +* **`let` **: bind a variable +* **`loop` **: loop unconditionally +* **`match` **: match a value to patterns +* **`mod` **: define a module +* **`move` **: make a closure take ownership of all its captures +* **`mut` **: denote mutability in references, raw pointers, or pattern bindings +* **`pub` **: denote public visibility in struct fields, `impl` blocks, or +modules +* **`ref` **: bind by reference +* **`return` **: return from function +* **`Self` **: a type alias for the type we are defining or implementing +* **`self` **: method subject or current module +* **`static` **: global variable or lifetime lasting the entire program +execution +* **`struct` **: define a structure +* **`super` **: parent module of the current module +* **`trait` **: define a trait +* **`true` **: Boolean true literal +* **`type` **: define a type alias or associated type +* **`union` **: define a union; is a keyword only when used in a union +declaration +* **`unsafe` **: denote unsafe code, functions, traits, or implementations +* **`use` **: bring symbols into scope +* **`where` **: denote clauses that constrain a type +* **`while` **: loop conditionally based on the result of an expression + +## Keywords Reserved for Future Use + +The following keywords do not yet have any functionality but are reserved by +Rust for potential future use: + +* `abstract` +* `become` +* `box` +* `do` +* `final` +* `macro` +* `override` +* `priv` +* `try` +* `typeof` +* `unsized` +* `virtual` +* `yield` + +## Raw Identifiers + +*Raw identifiers* are the syntax that lets you use keywords where they wouldn’t +normally be allowed. You use a raw identifier by prefixing a keyword with `r#`. + +For example, `match` is a keyword. If you try to compile the following function +that uses `match` as its name: + +Filename: src/main.rs + +``` +fn match(needle: &str, haystack: &str) -> bool { + haystack.contains(needle) +} +``` + +you’ll get this error: + +``` +error: expected identifier, found keyword `match` + --> src/main.rs:4:4 + | +4 | fn match(needle: &str, haystack: &str) -> bool { + | ^^^^^ expected identifier, found keyword +``` + +The error shows that you can’t use the keyword `match` as the function +identifier. To use `match` as a function name, you need to use the raw +identifier syntax, like this: + +Filename: src/main.rs + +``` +fn r#match(needle: &str, haystack: &str) -> bool { + haystack.contains(needle) +} + +fn main() { + assert!(r#match("foo", "foobar")); +} +``` + +This code will compile without any errors. Note the `r#` prefix on the function +name in its definition as well as where the function is called in `main`. + +Raw identifiers allow you to use any word you choose as an identifier, even if +that word happens to be a reserved keyword. This gives us more freedom to +choose identifier names, as well as lets us integrate with programs written in +a language where these words aren’t keywords. In addition, raw identifiers +allow you to use libraries written in a different Rust edition than your crate +uses. For example, `try` isn’t a keyword in the 2015 edition but is in the 2018 +and 2021 editions. If you depend on a library that is written using the 2015 +edition and has a `try` function, you’ll need to use the raw identifier syntax, +`r#try` in this case, to call that function from your 2021 edition code. See +Appendix E for more information on editions. + -- cgit v1.2.3