Optimistic Peach questions

Optimistic Peach answers

• How do I annotate rust variables' data type without assignment?
• Understanding `tt` in Rust's `macro_rules!` macros
• Why must be structure initialized in rust?
• Storing a module as a variable in rust
• How are sized types useful in Rust?
• How to implement fmt::Display on custom type?
• PhantomData type usage in rust
• Why does Rust allow calling functions via null pointers?
• How to create a thread local variable inside of a Rust struct?
• Why can't I import module from different file in same directory? [duplicate]