What is the advantage of doing so? Is it for cases where your source code is confidential but you want to sell access to your library?
Operating systems.
If there's a CVE in tokio, the OS could theoretically publish a patched version of tokio and all apps that depend on that end up using the fixed code.
As it stands now, the OS needs to publish updated versions of all rust apps that depend on tokio.
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Interoperating witt other languages without having to use C as a middleman?
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There is another thread complaining about compile times and tmp dir sizes.
Stable ABI dramatically improves the problem space there (without necessarily having anything to do with business model).