Re: [RFC PATCH 1/1] Add a type for errors

[Junio C Hamano <gitster@pobox.com>]

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> ....  It is designed to be passed and returned by value, not
> pointer, and it is possible to do so in two registers on 64-bit systems.
> Similar functionality works well for error types in Rust and for the
> standard library's lldiv_t, so this should not pose a problem.

It should not, in the sense that "any reasonable platform should be
able to pass two 64-bit word in a structure by value", but isn't it
optimizing for a wrong (i.e. have error) case?  In the case where
there is no error, a "negative return is error, zero is success",
with a pointer to "more detailed error info, in case the call
resulted in an error", would let us take branch based on a zero-ness
check on an integer in a machine-natural word, without even looking
at these two words in the struct.