chore: make some functions const

Cargo.toml

@@ -47,6 +47,7 @@ version_check = "0.9.5"
 module_name_repetitions = { level = "allow", priority = 1 }
 too_long_first_doc_paragraph = { level = "allow", priority = 1 } # Temporary
 pedantic = "deny"
+missing_const_for_fn = "deny"
 # Do not activate until Clippy issue #13356 is fixed
 #allow_attributes = "deny"
 

examples/sliding-puzzle.rs

@@ -75,7 +75,7 @@ impl Game {
     }
 
     // Compute the Manhattan distance between the piece at idx and its correct position.
-    fn distance(&self, idx: u8) -> u8 {
+    const fn distance(&self, idx: u8) -> u8 {
         let (actual_x, actual_y) = (Self::x(idx), Self::y(idx));
         let (correct_x, correct_y) = (
             Self::x(self.positions[idx as usize]),

src/grid.rs

@@ -124,13 +124,13 @@ impl Grid {
 
     /// Enable diagonal mode. Diagonal edges will be created between
     /// adjacent vertices.
-    pub fn enable_diagonal_mode(&mut self) {
+    pub const fn enable_diagonal_mode(&mut self) {
         self.diagonal_mode = true;
     }
 
     /// Disable diagonal mode. Only horizontal and vertical edges will
     /// be created between adjacent vertices.
-    pub fn disable_diagonal_mode(&mut self) {
+    pub const fn disable_diagonal_mode(&mut self) {
         self.diagonal_mode = false;
     }
 
@@ -310,7 +310,7 @@ impl Grid {
     /// Remove every existing vertex, and add all absent vertices.
     /// If you see the grid as a black and white array, imagine that
     /// the color are exchanged.
-    pub fn invert(&mut self) {
+    pub const fn invert(&mut self) {
         self.dense = !self.dense;
     }