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Consider a macro corresponding to Rust's ? operator #6552

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daira opened this issue Apr 14, 2023 · 1 comment · May be fixed by #6554
Open

Consider a macro corresponding to Rust's ? operator #6552

daira opened this issue Apr 14, 2023 · 1 comment · May be fixed by #6554
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daira commented Apr 14, 2023 •
edited

Example based on https://github.com/zcash/zcash/pull/6524/files#r1166886694 :

    auto maybeChangeAddr = /* a tl::expected<ChangeAddress, AddressResolutionError> */;
    if (maybeChangeAddr.has_value()) {
        changeAddr = maybeChangeAddr.value();
    } else {
        return tl::make_unexpected(maybeChangeAddr.error());
    }

It should be possible to write this as something like:

    changeAddr = unwrap { /* a tl::expected<ChangeAddress, AddressResolutionError> */ } or_return;

where the syntax using {} rather than parens is intended to call out that this can return and is not just a function call (while still being implementable).

See also:
@daira daira added the use case label Apr 14, 2023
@daira daira self-assigned this Apr 14, 2023
This was referenced Apr 14, 2023
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daira commented Apr 23, 2023

I ended up with a slightly different syntax that is a bit more robust to parsing problems (i.e. it gives less inexplicable errors if you get the syntax incorrect). The initial macro name needs to be try_unwrap because unwrap is also used in Boost headers, and that caused problems with the macro being expanded unintentionally. I also added some other variants as documented in #6554.

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Add a try_unwrap(...) or_return construct, similar to Rust's ? operator daira/zcash
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