dyn Write support removed?

[kornelski]

I've used to pass &mut dyn Write to the templates, but it does not compile any more due to <W> bound on template functions lacking ?Sized.

[kaj]

Yes, I simplified the output parameter from a rather complex trait bound that boild down to "mut any pointer mut that implements Write" to just &mut W where W: Write in #107 . I guess the ?Sized could be added back if there is a reason for it.

I mainly call the templates writing to a Vec<u8> for the body of a response. Do you call them in dynamic functions?

[kornelski]

yes, I'm writing to a compressed stream that has a complex type.

[kaj]

Ah, yes, there might be times when using a &dyn Write can better (or at least a log easier) than using an &impl Write and letting the compiler try to figure it all out. Ok, I'll try to add support for ?Sized back.

[kaj]

However, just adding ?Sized to W for the template functions messes up all calls to ToHtml::to_html in templates. So I have to figure out a way to do this. Maybe parameterize the ToHtml trait?

[wezm]

I think #107 also inhibits calling template functions on the out argument of ToHtml. To work around #78 I created this code:

pub struct ResponsiveImage<'asset> {
    asset: &'asset Asset,
    size: Resize,
}

impl<'asset> ResponsiveImage<'asset> {
    pub fn new(asset: &'asset Asset, size: Resize) -> Self {
        ResponsiveImage { asset, size }
    }
}

impl ToHtml for ResponsiveImage<'_> {
    fn to_html(&self, out: &mut dyn Write) -> io::Result<()> {
        let non_retina = self.asset.thumbnail_url(self.size);
        let retina = self.asset.thumbnail_url(self.size * 2);
        templates::responsive_image(out, non_retina, retina)
    }
}

Originally I was manually making write! calls in to_html but the code was a bit messy and I had to consider HTML escaping manually. So I thought I'd create a template and call the template from the impl. It fails to compile though:

error[E0277]: the size for values of type `dyn std::io::Write` cannot be known at compilation time
  --> src/utils.rs:71:37
   |
71 |         templates::responsive_image(out, non_retina, retina, "")
   |         --------------------------- ^^^ doesn't have a size known at compile-time
   |         |
   |         required by a bound introduced by this call
   |
   = help: the trait `Sized` is not implemented for `dyn std::io::Write`
note: required by a bound in `responsive_image_html`
  --> /home/wmoore/Projects/bellbird/target/debug/build/bellbird-73ced4a7b3ebeabd/out/templates/template_responsive_image_html.rs:8:30
   |
8  | pub fn responsive_image_html<W>(_ructe_out_: &mut W, non_retina: Origin, retina: Origin, alt: &str) -> io::Result<()>
   |                              ^ required by this bound in `responsive_image_html`
help: consider relaxing the implicit `Sized` restriction
  --> /home/wmoore/Projects/bellbird/target/debug/build/bellbird-73ced4a7b3ebeabd/out/templates/template_responsive_image_html.rs:9:15
   |
9  | where W: Write + ?Sized {
   |                ++++++++