Re:Optimizing Rust Struct Size
by eddyb on Saturday April 15, 2017 @07:01PM
(#14123330)
> now needs 'repr(C)'
It always has, we lint for this, and the Rust struct layout has been officially left unspecified (making assumptions based on it UB) from before 1.0, anyway.
> One would think that would be 'repr("C")', since here, "C" is neither a reserved word nor a variable, but, whatever.
Neither is 'repr' - they're both just identifiers in an attribute. #[attr("string literal")] is newer and still unstable (as part of the new macro system).
The bit array packing is something we've wanted to do for a long while, but it requires an opt-in along the lines of "disallow taking references to any (sub-byte) fields".
#[repr(packed)] is the same as the C equivalent, be it attribute or pragma, in that it only removes alignment padding and does nothing to booleans.
It always has, we lint for this, and the Rust struct layout has been officially left unspecified (making assumptions based on it UB) from before 1.0, anyway.
> One would think that would be 'repr("C")', since here, "C" is neither a reserved word nor a variable, but, whatever.
Neither is 'repr' - they're both just identifiers in an attribute. #[attr("string literal")] is newer and still unstable (as part of the new macro system).
The bit array packing is something we've wanted to do for a long while, but it requires an opt-in along the lines of "disallow taking references to any (sub-byte) fields".
#[repr(packed)] is the same as the C equivalent, be it attribute or pragma, in that it only removes alignment padding and does nothing to booleans.