solution.md

Solution

{{#include exercise.rs:solution}}

• Pattern Matching: We use match to handle the different variants of the Expression enum. This ensures we cover all possible cases.
• Destructuring: The pattern Expression::Op { op, left, right } destructures the Op variant, giving us access to its inner fields.
• Recursion: Since Expression is a recursive data structure, eval is a recursive function. We call eval(*left) and eval(*right) to compute the values of the sub-expressions.
• Smart Pointers (Box): The left and right fields are of type Box<Expression>. Box puts the value on the heap. The * operator dereferences the box, moving the inner Expression out so it can be passed by value to the recursive eval calls.

Details

• Mention that Box is necessary because Expression has infinite size otherwise (it contains itself). Box provides a fixed size (pointer size) for the recursive fields.
• Discuss integer division behavior (truncation) for Operation::Div since we are using integers.