example: add example for S3 ListObjectsV2 with paginator

[jasdel]

Adds a simple example for Amazon S3 ListObjectsV2 API call with a hand written paginator. Paginator should be updated to use the SDK's generated paginators once available.

[skotambkar]

Minor comments

[JordonPhillips]

This should probably have a page size parameter

[jasdel]

Page size is currently a parameter of the s3.ListObjectsV2Input type. I'm not sure if this should be duplicated here, since it is an optional parameter already present in the input type. I'd think if the user wants to specify this value with a custom size then it should be done on the input value.

What are your thoughts on this?

[JordonPhillips]

The reason it's an attribute on the paginator trait is so that clients can expose a consistent interface for providing that value. Between operations and services the member could be any number of things, like Limit, MaxItems, PageSize, etc.

[jasdel]

yup though its still an optional parameter in all APIs. By putting it as a parameter on the constructor the SDK is paginator is effectively making it required. The handling for required, but not required parameter, would be to treat the limit parameter as unset if its value is 0. Minor, but this approach still requires the user to pass in a 0 for the default behavior.

[JordonPhillips]

Well you can always make a pointer so people pass it in as nil, or have a function to set it as a second step that takes a non-pointer

[jasdel]

Adding functional options to add configuration to the paginator might be a good way to do this.

type ListObjectsV2PaginatorOptions struct {
     Limit int32 // generic name for all paginators
}

func NewListObjectsV2Paginator(client ListObjectsV2APIClient, params *s3.ListObjectsV2Input,
     optFns ...func(*ListObjectsV2PaginatorOptions)

p := s3.NewListObjectsV2Paginator(client, params, func(o *ListObjectsV2PaginatorOptions) {
      o.Limit = 10
})

or instead of ListObjectsV2PaginatorOptions could put Limit directly on the paginator, but that probably makes it easy to cause unexpected bugs by implying the value can be changed after the paginator is created.

[jasdel]

updated to include this pattern 👍