I'm not sure I've ever seen this conversion before for other traits. What's the rationale for it?

I'm not sure I've ever seen this conversion before for other traits. What's the rationale for it?

As mentioned in the comment, this allows you to build aBox<dyn ToSql> from any type and can be used to create aVec of these values that can be passed to thequery_raw().

This is necessary in order to build these values e.g. dynamically and I couldn't find any other way to do so.
The example ofquery_raw uses onlyStrings (1 type) so this issue is not present.

Example:

// These parameters can now come from e.g. another function call and can be mixed typeslet params: Vec<Box<dyn ToSql + Sync + Send>> = vec![    "first param".into(),    42.into(),];let mut it = client.query_raw(    "SELECT foo FROM bar WHERE biz = $1 AND baz = $2",    params,).await?;

Can't you just call Box::new yourself?

Can't you just call Box::new yourself?

Maybe I just don't know how to do the casting since I get a type error:

17 |         pub fn get_key(&self, key: AllowedKey) -> Option<Box<dyn ToSql + Sync + Send>> {   |                                                   ------------------------------------ expected `std::option::Option<Box<(dyn ToSql + Send + Sync + 'static)>>` because of return type18 |             match key {19 |                 AllowedKey::CampaignId => self.campaign_id.map(Box::new),   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn ToSql`, found struct `CampaignId`   |   = note: expected enum `std::option::Option<Box<(dyn ToSql + Send + Sync + 'static)>>`              found enum `std::option::Option<Box<CampaignId>>`

I've also tried the following but then I get an error because ofSized requirements forBox::new

self.campaign_id.map(|s|Box::new(sas_)),

Without seeing the rest of the code I can't be 100% sure, but one of these should work:self.campaign_id.map(|s| Box::new(s)) orself.campaign_id.map(|s| Box::new(s) as _).

Without seeing the rest of the code I can't be 100% sure, but one of these should work:self.campaign_id.map(|s| Box::new(s)) orself.campaign_id.map(|s| Box::new(s) as _).

Here are links to the playground with 3 non-working examples:

• Box::new(value as _):https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=042514743d7600b0b5f1cfcbaed37a51

• Box::new(value.into()) (this is closest but it complains aboutSized):https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=042514743d7600b0b5f1cfcbaed37a51

• And justBox::new(value):https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=097653481061736cf66bddb06135efe1

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=26af9ee9d1ab04b26a506c8b33966769

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=26af9ee9d1ab04b26a506c8b33966769

Good point! Didn't think of this 😄