Solution

# // Copyright 2023 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
{{#include exercise.rs:solution}}

• Array Types: The type [[i32; 3]; 3] represents an array of size 3, where each element is itself an array of 3 i32s. This is how multi-dimensional arrays are typically represented in Rust.
• Initialization: We initialize result with zeros ([[0; 3]; 3]) before filling it. Rust requires all variables to be initialized before use; there is no concept of "uninitialized memory" in safe Rust.
• Copy Semantics: Arrays of Copy types (like i32) are themselves Copy. When we pass matrix to the function, it is copied by value. The result variable is a new, separate array.
• Iteration: We use standard for loops with ranges (0..3) to iterate over indices. Rust also has powerful iterators, which we will see later, but indexing is straightforward for this matrix transposition.

• Mention that [i32; 3] is a distinct type from [i32; 4]. Array sizes are part of the type signature.
• Ask students what would happen if they tried to return matrix directly after modifying it (if they changed the signature to mut matrix). (Answer: It would work, but it would return a modified copy, leaving the original in main unchanged).