Implementing From<Arc<str>> for SmolStr and From<SmolStr> for Arc<str>

[msdrigg]

Solves #57

• Adding implementations to convert SmolStr to and from Arc<str>
• Also adding one test to verify

---

The From<SmolStr> implementation is good. It saves an alloc in the Repr::Heap case, and allocates in the stack cases. It should be good to go.

The From<Arc<str>> does currently does not check for inline-able or whitespace strings. All Arc<str> become Repr::Heap. If this is a problem, could I get some feedback on how to solve it? Currently only SmolStr::new contains the code to detect inlines and whitespaces, so there are two options

• I could duplicate this whole code block into the From impl
• Or I could split it off into a separate function like fn new_on_stack(text: &str) -> Option<SmolStr> and then use that in Smol::new and From<Arc<str>>

[Veykril]

We should check the length for this and not use heap if small enough. I'd say let's just go with your second outlined option for that to reduce code duplication

[msdrigg]

Now it only goes on the stack if it can

[lnicola]

r? @Veykril