[native] change params and types to satisfy cxx requirements
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Authored by varun on Aug 23 2022, 10:43 PM.

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tomek
• karol
atul

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rCOMMb055e9dcb91f: [native] change params and types to satisfy cxx requirements

Summary

Changed auth_type to an i32 to make it easier to pass across the FFI boundary. Also changed a return type to a String for the same reason.

Depends on D4933

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cargo build

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Event Timeline

varun created this revision.Aug 23 2022, 10:43 PM

Herald added subscribers: • abosh, ashoat. · View Herald TranscriptAug 23 2022, 10:43 PM

varun added a child revision: D4935: [native] make output a static library.Aug 23 2022, 10:47 PM

Harbormaster completed remote builds in B11563: Diff 15899.Aug 23 2022, 10:52 PM

varun requested review of this revision.Aug 23 2022, 10:52 PM

Changed auth_type to an i32 to make it easier to pass across the FFI boundary.

Is it a good practice to use i32 instead of enum? How hard is it to pass an enum?

native/cpp/CommonCpp/grpc/grpc_client/src/lib.rs
88 ↗	(On Diff #15899)	`auth_type` is already `i32` here, so why do we need to cast it?

This revision now requires changes to proceed.Aug 24 2022, 2:57 AM

remove unnecessary cast

In D4934#142918, @tomek wrote:

Changed auth_type to an i32 to make it easier to pass across the FFI boundary.

Is it a good practice to use i32 instead of enum? How hard is it to pass an enum?

It's not a great practice but it's hard to pass an enum. If the enum is defined in the ffi module, the compiler complains:

non-primitive cast: `ffi::AuthType` as `i32`
an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object

And if I try to define it in the Rust library, the compiler complains about passing opaque Rust types by value.

I can explore a better solution and revisit this later, if that works for you.

native/cpp/CommonCpp/grpc/grpc_client/src/lib.rs
88 ↗	(On Diff #15899)	we don't! good catch

Harbormaster completed remote builds in B11602: Diff 15950.Aug 24 2022, 8:25 PM

In D4934#143266, @varun wrote:
In D4934#142918, @tomek wrote:

Changed auth_type to an i32 to make it easier to pass across the FFI boundary.

Is it a good practice to use i32 instead of enum? How hard is it to pass an enum?

It's not a great practice but it's hard to pass an enum. If the enum is defined in the ffi module, the compiler complains:
non-primitive cast: `ffi::AuthType` as `i32`
an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
And if I try to define it in the Rust library, the compiler complains about passing opaque Rust types by value.

I can explore a better solution and revisit this later, if that works for you.

Yeah, a small research sounds like a good idea. The safer we make this code, the less problems we will have in the future. A quick search gave me this https://rust-lang.github.io/unsafe-code-guidelines/layout/enums.html#repr-annotations-accepted-on-enums - not sure, but it might be helpful.