From 42fa7df38cea93d1a1991b7aa085a7a57b2800fa Mon Sep 17 00:00:00 2001 From: Josh Triplett Date: Mon, 31 Jul 2023 16:07:09 -0700 Subject: [PATCH] style-guide: Expand documentation on `as` casts (mostly like a binary operator) `as` casts currently get formatted like a binary operator, except that the second line can stack several `as` casts rather than breaking them each onto their own line. Merge `as` into a subsection of the binary operators section, and then go into detail on the one difference between `as` formatting and binary operator formatting. --- src/doc/style-guide/src/expressions.md | 28 ++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/src/doc/style-guide/src/expressions.md b/src/doc/style-guide/src/expressions.md index 32c604f9f3e10..91dd3d2224abe 100644 --- a/src/doc/style-guide/src/expressions.md +++ b/src/doc/style-guide/src/expressions.md @@ -328,6 +328,26 @@ foo_bar Prefer line-breaking at an assignment operator (either `=` or `+=`, etc.) rather than at other binary operators. +### Casts (`as`) + +Format `as` casts like a binary operator. In particular, always include spaces +around `as`, and if line-breaking, break before the `as` (never after) and +block-indent the subsequent line. Format the type on the right-hand side using +the rules for types. + +However, unlike with other binary operators, if chaining a series of `as` casts +that require line-breaking, and line-breaking before the first `as` suffices to +make the remainder fit on the next line, don't break before any subsequent +`as`; instead, leave the series of types all on the same line: + +```rust +let cstr = very_long_expression() + as *const str as *const [u8] as *const std::os::raw::c_char; +``` + +If the subsequent line still requires line-breaking, break and block-indent +before each `as` as with other binary operators. + ## Control flow Do not include extraneous parentheses for `if` and `while` expressions. @@ -421,14 +441,6 @@ assert_eq!( ); ``` -## Casts (`as`) - -Put spaces before and after `as`: - -```rust -let cstr = "Hi\0" as *const str as *const [u8] as *const std::os::raw::c_char; -``` - ## Chains of fields and method calls A chain is a sequence of field accesses, method calls, and/or uses of the try