::ext-trait

Annotation to easily define ad-hoc / one-shot extension traits.

Examples

• Also

  #[macro_use]
  extern crate ext_trait;
  
  #[extension(trait Also)]
  impl<T> T {
      fn also (mut self, f: impl FnOnce(&mut Self))
        -> Self
      {
          f(&mut self);
          self
      }
  }
  
  fn main ()
  {
      use ::std::{collections::HashMap, ops::Not};
  
      let /* immut */ map = HashMap::with_capacity(2).also(|m| {
          m.insert("foo", 42);
          m.insert("bar", 27);
      });
      assert!(map.contains_key("foo"));
      assert!(map.contains_key("bar"));
      assert!(map.contains_key("baz").not());
  }
  

• WithPath

  #[macro_use]
  extern crate ext_trait;
  
  use ::std::{error::Error, path::{Path, PathBuf}};
  
  #[extension(trait WithPath)]
  impl PathBuf {
      fn with (mut self, segment: impl AsRef<Path>)
        -> PathBuf
      {
          self.push(segment);
          self
      }
  }
  
  fn main ()
    -> Result<(), Box<dyn Error>>
  {
      let some_dir = PathBuf::from(::std::env::var("MY_LIB_SOME_DIR")?);
      // Contrary to chaining `.join()`, this reuses the memory!
      let some_subdir = some_dir.with("some").with("sub").with("dir");
      // …
      Ok(())
  }
  

• Context

  #[macro_use]
  extern crate ext_trait;
  
  use ::std::{error::Error, fmt::Display};
  
  #[extension(trait Context)]
  impl<Ok, Err : Display> Result<Ok, Err> {
      fn context (self, prefix: impl Display)
        -> Result<Ok, String>
      {
          self.map_err(|err| format!("{}: {}", prefix, err))
      }
  }
  
  fn main ()
    -> Result<(), Box<dyn Error>>
  {
      let file_contents =
          ::std::fs::read_to_string("some/file")
              .context("Error when opening some/file")?
      ;
      // …
      Ok(())
  }
  

Similar to https://docs.rs/extension-trait, but for the following:

Features

• Supports generics (see Context)

• search/grep 'trait TraitName'-friendly!