Page Comparison

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(assuming I understand this, which is an if, a small if, but an if nonetheless)

Part A

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We can implement methods directly on shared reference types themselves. There is no deref coercion then when called on a shared reference that is of that shared reference type (playground)

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Note how the implementation is for the ref string slice type, not the primitive string slice type.

Part B

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1. Consider two traits

   1. From<String>

   2. From<&'a static str>

2. The enum Cow<'astatic, str> implements both traits

   1. Cow has the associated function
      fn from(s: String) → Cow<'astatic, str>

   2. Cow has another associated function
      fn from(s: &'a static str) → Cow<'static, str>

3. Consider another trait

   1. Into<Cow<'static, str>>

4. A From implementation implies that there is a

   , str>

5. Therefore String implements<

6. Consider the additional trait

   Into<Cow<'a, str>>

   corresponding Into implementation. There is a blanket implementation of Into in the standard library. My guess is that the following code is the blanket implementation

   Code Block
   language rust
   impl<T,U> Into<U> for T where U: From<T> { fn into(self) -> U { U::from(self) } }

7. Therefore String implements the Into<Cow<'static,str>> trait

   Code Block
   language rust
   impl Into<Cow<'static, str>> for String { fn into(self) -> Cow<'static, str> { ... } }

8. 
   

1. Consider the additional trait

2. String automatically implements Into, as does str, given that the From traits are implemented

3. Both String and str implement Into with a method of the following form

   1. fn into(self) → Cow<a', str>

4. In the first four arms of the match expression, there are string literals upon which the method into() is called. We know the methods must have a return type of Cow<'static, str>.

5. A string literal is of type &str, a shared reference to a string slice.

6. When applying the method into(), the string literal is dereferenced into a string slice str

7. Then the method into() can be applied on the str. We have already seen that this method exists.