Figure out what to do with flexible array members

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Refactor
Clarity
Needs clarification
Activity status
Quiet
Tech stack
c, rust
Domain
operating-systems

Research direction

Start by locating the existing Rust definitions that map C flexible array members to public [T; 0] fields, then compare that pattern with unsized [c_char] fields and the listed size_of, offset_of, and reference-use cases. Done means reaching and documenting a decision for the 1.0 representation, with its ABI and usability tradeoffs justified.

Written by the indexing model from the issue text.

Description

C-discussion

A number of C structures make use of a flexible array member:

struct sockaddr {
     sa_family_t     sa_family;      /* Address family */
     char            sa_data[];      /* Socket address */
 };

When mapped to Rust, most of these are a public field of type [T; 0]. We could instead map them to Rust unsized [c_char] fields.

The current pattern has a few advantages over using DSTs:

  • size_of works to get you the base size
  • You can offset_of the field to get the start of the array if you need it
  • You can work with the type through references, they don't need to be constructed as fat pointers
  • Rust's flexible array members aren't all that convenient to work with

I expect we'll probably want to stick with the current pattern, but it's worth double checking that there isn't something better for 1.0.

Dominant language
Rust
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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