1.15.1. Static Dispatch
What happens when we compile generic code?
The compiler copies part of the type or function for each T (for each concrete type), so that each type has its own function. This process is called monomorphization. (Calling methods on a dyn Trait is different: that uses dynamic dispatch, covered later in this article.)
When you build Vec<i32> or HashMap<String, bool>, the compiler copies the generic type and all of its implementation blocks. For example, Vec<i32> replaces the T in Vec<T> with i32, effectively making a full copy of Vec, with every T replaced by i32.
In other words, the compiler replaces the generic parameters of an instance with concrete types. Note that the compiler does not literally duplicate and paste everything; it only copies the code you actually use.
