Mention ADT and zero-cost abstractions among modern features

src/why-rust/modern.md

@@ -7,6 +7,7 @@ Rust is built with all the experience gained in the last 40 years.
 * Enums and pattern matching.
 * Generics.
 * No overhead FFI.
+* Zero-cost abstractions.
 
 ## Tooling
 
@@ -18,6 +19,15 @@ Rust is built with all the experience gained in the last 40 years.
 
 Key points:
 
+* Zero-cost abstractions, similar to C++, means that you don't have to 'pay'
+  for higher-level programming constructs with memory or CPU. For example,
+  writing a loop using `for` should result in roughly the same low level
+  instructions as using the `.iter().fold()` construct.
+
+* It may be worth mentioning that Rust enums are 'Algebraic Data Types', also
+  known as 'sum types', which allow the type system to express things like
+  `Option<T>` and `Result<T, E>`.
+
 * Remind people to read the errors --- many developers have gotten used to
   ignore lengthly compiler output. The Rust compiler is significantly more
   talkative than other compilers. It will often provide you with _actionable_