it worked! From dyn Tag into any concrete tag without cloning

.github/workflow/main.yml

@@ -0,0 +1,64 @@
+on: [push, pull_request]
+
+name: Continuous integration
+
+jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+
+  test:
+    name: Test Suite
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - run: rustup component add rustfmt
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - run: rustup component add clippy
+      - uses: actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: -- -D warnings

CHANGELOG.md

@@ -1,3 +1,11 @@
+## [0.2.718] 2020-10-27
+
+- downcasting
+
+## [0.2.71] 2020-10-27
+
+- Remove use of `Cow`
+
 ## [0.2.5] 2020-10-27
 
 - Naive implementation of config

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "audiotags"
-version = "0.2.71"
+version = "0.2.718"
 authors = ["Tianyi <ShiTianyi2001@outlook.com>"]
 edition = "2018"
 description = "Unified IO for different types of audio metadata"
@@ -14,4 +14,4 @@ id3 = "0.5.1"
 mp4ameta = "0.6"
 metaflac = "0.2"
 thiserror = "1.0.21"
-audiotags-dev-macro = {path = "./audiotags-dev-macro", version = "0.1.2"}
+audiotags-dev-macro = {path = "./audiotags-dev-macro", version = "0.1"}

audiotags-dev-macro/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "audiotags-dev-macro"
-version = "0.1.2"
+version = "0.1.3"
 authors = ["Tianyi <ShiTianyi2001@outlook.com>"]
 edition = "2018"
 description = "macros used during the development of audiotags"

audiotags-dev-macro/src/lib.rs

@@ -14,7 +14,7 @@ macro_rules! impl_audiotag_config {
 
 #[macro_export]
 macro_rules! impl_tag {
-    ($tag:ident , $inner:ident) => {
+    ($tag:ident , $inner:ident, $tag_type:expr) => {
         #[derive(Default)]
         pub struct $tag {
             inner: $inner,
@@ -33,13 +33,24 @@ macro_rules! impl_tag {
         }
         impl_audiotag_config!($tag);
 
+        use std::any::Any;
+
         impl IntoAnyTag for $tag {
             fn into_anytag(&self) -> AnyTag<'_> {
                 self.into()
             }
-            fn into_any(&self) -> &dyn std::any::Any {
+            fn into_any(&self) -> &dyn Any {
                 self
             }
+            fn into_any_mut(&mut self) -> &mut dyn Any {
+                self
+            }
+        }
+
+        impl $tag {
+            pub(crate) fn into_any_owned(self) -> Box<dyn Any> {
+                Box::new(self)
+            }
         }
 
         impl AudioTag for $tag {}
@@ -61,23 +72,45 @@ macro_rules! impl_tag {
 
         // downcasting
 
-        impl<'a> std::convert::TryFrom<&'a Box<dyn AudioTag>> for &'a $tag {
-            type Error = crate::Error;
-            fn try_from(inp: &'a Box<dyn AudioTag>) -> crate::Result<Self> {
-                inp.into_any()
-                    .downcast_ref::<$tag>()
-                    .ok_or(crate::Error::DowncastError)
+        // impl<'a> std::convert::TryFrom<&'a Box<dyn AudioTag>> for &'a $tag {
+        //     type Error = crate::Error;
+        //     fn try_from(inp: &'a Box<dyn AudioTag>) -> crate::Result<Self> {
+        //         inp.into_any()
+        //             .downcast_ref::<$tag>()
+        //             .ok_or(crate::Error::DowncastError)
+        //     }
+        // }
+
+        impl From<Box<dyn AudioTag>> for $tag {
+            fn from(inp: Box<dyn AudioTag>) -> Self {
+                let mut inp = inp;
+                if let Some(t_refmut) = inp.into_any_mut().downcast_mut::<$tag>() {
+                    let t = std::mem::replace(t_refmut, $tag::new()); // TODO: can we avoid creating the dummy tag?
+                    t
+                } else {
+                    let mut t = inp.into_tag($tag_type);
+                    let t_refmut = t.into_any_mut().downcast_mut::<$tag>().unwrap();
+                    let t = std::mem::replace(t_refmut, $tag::new());
+                    t
+                }
             }
         }
 
-        impl std::convert::TryFrom<Box<dyn AudioTag>> for $inner {
-            type Error = crate::Error;
-            fn try_from(inp: Box<dyn AudioTag>) -> crate::Result<Self> {
-                let t: &$tag = inp
-                    .into_any()
-                    .downcast_ref::<$tag>()
-                    .ok_or(crate::Error::DowncastError)?;
-                Ok(t.into())
+        // impl std::convert::TryFrom<Box<dyn AudioTag>> for $inner {
+        //     type Error = crate::Error;
+        //     fn try_from(inp: Box<dyn AudioTag>) -> crate::Result<Self> {
+        //         let t: &$tag = inp
+        //             .into_any()
+        //             .downcast_ref::<$tag>()
+        //             .ok_or(crate::Error::DowncastError)?;
+        //         Ok(t.into())
+        //     }
+        // }
+
+        impl std::convert::From<Box<dyn AudioTag>> for $inner {
+            fn from(inp: Box<dyn AudioTag>) -> Self {
+                let t: $tag = inp.into();
+                (&t).into()
             }
         }
     };

rtfm/_bookdown.yml

@@ -1,6 +1,7 @@
 book_filename: "audiotags"
+rmd_files: ["index.Rmd", "simple.Rmd", "convert.Rmd", "anytag.Rmd", "downcast.Rmd"]
 output_dir: "../docs"
 delete_merged_file: true
-language:
-  ui:
-    chapter_name: "Chapter "
+# language:
+#   ui:
+#     chapter_name: "Chapter "

rtfm/downcast.Rmd

@@ -21,7 +21,7 @@ fn main() {
         .expect("Fail to read!");
     assert_eq!(id3tag_reload.title(), Some("title from metaflac::Tag"));
 
-    let mut id3tag_inner: id3::Tag = id3tag_reload.try_into().unwrap();
+    let mut id3tag_inner: id3::Tag = id3tag_reload.into();
     // this would fail if `id3tag_reload` isn't really a id3 tag.
 
     let timestamp = id3::Timestamp {

rtfm/index.Rmd

@@ -4,7 +4,7 @@ author: "Tianyi Shi"
 date: "`r Sys.Date()`"
 site: bookdown::bookdown_site
 documentclass: book
-bibliography: [book.bib, packages.bib]
+bibliography: [book.bib]
 biblio-style: apalike
 link-citations: yes
 description: "This is the manual of the Rust crate 'audiotags'"

rtfm/packages.bib

@@ -1,85 +0,0 @@
-@Manual{R-base,
-  title = {R: A Language and Environment for Statistical Computing},
-  author = {{R Core Team}},
-  organization = {R Foundation for Statistical Computing},
-  address = {Vienna, Austria},
-  year = {2020},
-  url = {https://www.R-project.org/},
-}
-
-@Manual{R-bookdown,
-  title = {bookdown: Authoring Books and Technical Documents with R Markdown},
-  author = {Yihui Xie},
-  year = {2020},
-  note = {R package version 0.21},
-  url = {https://github.com/rstudio/bookdown},
-}
-
-@Manual{R-knitr,
-  title = {knitr: A General-Purpose Package for Dynamic Report Generation in R},
-  author = {Yihui Xie},
-  year = {2020},
-  note = {R package version 1.30},
-  url = {https://yihui.org/knitr/},
-}
-
-@Manual{R-rmarkdown,
-  title = {rmarkdown: Dynamic Documents for R},
-  author = {JJ Allaire and Yihui Xie and Jonathan McPherson and Javier Luraschi and Kevin Ushey and Aron Atkins and Hadley Wickham and Joe Cheng and Winston Chang and Richard Iannone},
-  year = {2020},
-  note = {R package version 2.4},
-  url = {https://github.com/rstudio/rmarkdown},
-}
-
-@Book{bookdown2016,
-  title = {bookdown: Authoring Books and Technical Documents with {R} Markdown},
-  author = {Yihui Xie},
-  publisher = {Chapman and Hall/CRC},
-  address = {Boca Raton, Florida},
-  year = {2016},
-  note = {ISBN 978-1138700109},
-  url = {https://github.com/rstudio/bookdown},
-}
-
-@Book{knitr2015,
-  title = {Dynamic Documents with {R} and knitr},
-  author = {Yihui Xie},
-  publisher = {Chapman and Hall/CRC},
-  address = {Boca Raton, Florida},
-  year = {2015},
-  edition = {2nd},
-  note = {ISBN 978-1498716963},
-  url = {https://yihui.org/knitr/},
-}
-
-@InCollection{knitr2014,
-  booktitle = {Implementing Reproducible Computational Research},
-  editor = {Victoria Stodden and Friedrich Leisch and Roger D. Peng},
-  title = {knitr: A Comprehensive Tool for Reproducible Research in {R}},
-  author = {Yihui Xie},
-  publisher = {Chapman and Hall/CRC},
-  year = {2014},
-  note = {ISBN 978-1466561595},
-  url = {http://www.crcpress.com/product/isbn/9781466561595},
-}
-
-@Book{rmarkdown2018,
-  title = {R Markdown: The Definitive Guide},
-  author = {Yihui Xie and J.J. Allaire and Garrett Grolemund},
-  publisher = {Chapman and Hall/CRC},
-  address = {Boca Raton, Florida},
-  year = {2018},
-  note = {ISBN 9781138359338},
-  url = {https://bookdown.org/yihui/rmarkdown},
-}
-
-@Book{rmarkdown2020,
-  title = {R Markdown Cookbook},
-  author = {Yihui Xie and Christophe Dervieux and Emily Riederer},
-  publisher = {Chapman and Hall/CRC},
-  address = {Boca Raton, Florida},
-  year = {2020},
-  note = {ISBN 9780367563837},
-  url = {https://bookdown.org/yihui/rmarkdown-cookbook},
-}
-

rtfm/style.css

@@ -14,15 +14,6 @@ pre code {
 }
 
 
-
-@font-face {
-  font-family: 'Merriweather';
-  font-style: normal;
-  font-weight: 400;
-  src: local('Merriweather'), local('Merriweather-Regular'),
-       url('https://tianyishi2001.github.io/ox/fonts/merriweather-v13-latin-regular.woff2') format('woff2'),
-       url('https://tianyishi2001.github.io/ox/fonts/merriweather-v13-latin-regular.woff') format('woff');
-}
 @font-face {
   font-family: 'Lato';
   font-style: normal;

src/components/flac_tag.rs

@@ -3,7 +3,7 @@ use metaflac;
 
 pub use metaflac::Tag as FlacInnerTag;
 
-impl_tag!(FlacTag, FlacInnerTag);
+impl_tag!(FlacTag, FlacInnerTag, TagType::Flac);
 
 impl<'a> From<AnyTag<'a>> for FlacTag {
     fn from(inp: AnyTag<'a>) -> Self {

src/components/id3_tag.rs

@@ -3,7 +3,7 @@ use id3;
 
 pub use id3::Tag as Id3v2InnerTag;
 
-impl_tag!(Id3v2Tag, Id3v2InnerTag);
+impl_tag!(Id3v2Tag, Id3v2InnerTag, TagType::Id3v2);
 
 impl<'a> From<&'a Id3v2Tag> for AnyTag<'a> {
     fn from(inp: &'a Id3v2Tag) -> Self {

src/components/mp4_tag.rs

@@ -3,7 +3,7 @@ use mp4ameta;
 
 pub use mp4ameta::Tag as Mp4InnerTag;
 
-impl_tag!(Mp4Tag, Mp4InnerTag);
+impl_tag!(Mp4Tag, Mp4InnerTag, TagType::Mp4);
 
 impl<'a> From<&'a Mp4Tag> for AnyTag<'a> {
     fn from(inp: &'a Mp4Tag) -> Self {

src/lib.rs

@@ -27,7 +27,7 @@
 //! struct. However, this is going to be a lot of work. I might be able to implement them, but it will be no
 //! sooner than the Christmas vacation.
 //!
-//! See [README](https://github.com/TianyiShi2001/audiotags) for some examples.
+//! Read the [manual](https://tianyishi2001.github.io/audiotags) for some examples.
 
 pub(crate) use audiotags_dev_macro::*;
 

src/traits.rs

@@ -151,4 +151,18 @@ pub trait IntoAnyTag {
         }
     }
     fn into_any(&self) -> &dyn std::any::Any;
+    fn into_any_mut(&mut self) -> &mut dyn std::any::Any;
 }
+
+// struct BoxedAudioTagWrapper {
+//     inner: Box<dyn AudioTag>,
+// }
+
+// impl<'a> BoxedAudioTagWrapper {
+//     fn into_tag<T>(self) -> T
+//     where
+//         T: From<AnyTag<'a>>,
+//     {
+//         self.inner.into_anytag().into()
+//     }
+// }

tests/inner.rs

@@ -17,7 +17,8 @@ fn test_inner() {
         .expect("Fail to read!");
     assert_eq!(id3tag_reload.title(), Some("title from metaflac::Tag"));
 
-    let mut id3tag_inner: id3::Tag = id3tag_reload.try_into().unwrap();
+    // let id3tag: Id3v2Tag = id3tag_reload.into();
+    let mut id3tag_inner: id3::Tag = id3tag_reload.into();
     let timestamp = id3::Timestamp {
         year: 2013,
         month: Some(2u8),