[request]: I wish DynamoDB fluent builders implemented `Clone`

[dcormier]

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It would help me if DynamoDB fluent builders implemented Clone.

I've encountered two points where I've wanted to be able to clone fluent builders.

1. When trying to scan a table and go through all the pages.
   • It would be helpful to be able to call .set_exclusive_start_key(...) and clone the Scan instance before calling .send() to get the next page so that the Scan instance could be re-used to get the next page.
   • Currently, I have to build a new Scan instance for every page.
2. When updating many items, and you encounter errors that should be retried (500s, ThrottlingExceptions, etc).
   • It would be nice to be able to clone the UpdateItem and just retry the .send() call.
   • Currently, I have to build a new UpdateItem for every attempt.

I'm sure I will find more cases when being able to clone a struct from that module would be useful. I've only been using the SDK for two days.

[rcoh]

this is a great idea!

[rcoh]

mentorship is available for this issue

[dcormier]

I'm interested. I'll take a look at smithy-rs.

[dcormier]

Eh. Less interested. I'll let someone else have it.

[Jacco]

@rcoh

I'd like to have a go at it :-) (Am new at rust and kotlin though).

I thought of conditionally adding the following code to FluentClientDecorator.kt in the FluentClientGenerator:

                    rustTemplate(
                        """
                        /// Creates a clone from another `${operationSymbol.name}`.
                        pub fn clone_from(self, other: Self) -> Self {
                            Self { handle: self.handle.clone(), inner: other.inner.clone() }
                        }
                        """,
                    )

I don't know if this is how it is desired.

I also don't know how to properly make it conditional. It needs to be conditional because not all of the inner members of the operations in the sdk can be cloned.

Regards, Jacco

[rcoh]

did you try adding #[derive(Clone)] bound here? https://github.com/awslabs/smithy-rs/blob/cf2034f9cf7a69d1360afa0042d2a08af2a18773/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/FluentClientDecorator.kt#L406

[Jacco]

@rcoh Yes I tried that first but many inner are not Clone.

[rcoh]

ah right because of ByteStream. You'll need to use a tactic like this: https://github.com/awslabs/smithy-rs/blob/c8a940be89ebe07200800a0d05fa58863be45b3d/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/BuilderGenerator.kt#L164-L166

That way we can generate the identical derives that Inner has. You can use operationShape.inputShape(model).expectRustMetadata() to pull the right piece of information

[Jacco]

@rcoh

I made a PR :-) Hope it is OK.