refactor: Rewrite manual let-else

src/codecs/gif.rs

@@ -308,19 +308,16 @@ impl<R: Read> Iterator for GifFrameIterator<R> {
         // correct storage requirement if the result does not fit in `usize`.
         // on the other hand, `ImageBuffer::from_raw` detects overflow and
         // reports by returning `None`.
-        let mut frame_buffer = match ImageBuffer::from_raw(frame.width, frame.height, vec) {
-            Some(frame_buffer) => frame_buffer,
-            None => {
-                return Some(Err(ImageError::Unsupported(
-                    UnsupportedError::from_format_and_kind(
-                        ImageFormat::Gif.into(),
-                        UnsupportedErrorKind::GenericFeature(format!(
-                            "Image dimensions ({}, {}) are too large",
-                            frame.width, frame.height
-                        )),
-                    ),
-                )))
-            }
+        let Some(mut frame_buffer) = ImageBuffer::from_raw(frame.width, frame.height, vec) else {
+            return Some(Err(ImageError::Unsupported(
+                UnsupportedError::from_format_and_kind(
+                    ImageFormat::Gif.into(),
+                    UnsupportedErrorKind::GenericFeature(format!(
+                        "Image dimensions ({}, {}) are too large",
+                        frame.width, frame.height
+                    )),
+                ),
+            )));
         };
 
         // blend the current frame with the non-disposed frame, then update

src/codecs/pnm/decoder.rs

@@ -540,17 +540,14 @@ trait HeaderReader: Read {
             }
         }
 
-        let (h, w, d, m) = match (height, width, depth, maxval) {
-            (Some(h), Some(w), Some(d), Some(m)) => (h, w, d, m),
-            _ => {
-                return Err(DecoderError::HeaderLineMissing {
-                    height,
-                    width,
-                    depth,
-                    maxval,
-                }
-                .into())
+        let (Some(h), Some(w), Some(d), Some(m)) = (height, width, depth, maxval) else {
+            return Err(DecoderError::HeaderLineMissing {
+                height,
+                width,
+                depth,
+                maxval,
             }
+            .into());
         };
 
         let tupltype = match tupltype {

src/flat.rs

@@ -421,9 +421,8 @@ impl SampleLayout {
         let idx_x = x.checked_mul(self.width_stride);
         let idx_y = y.checked_mul(self.height_stride);
 
-        let (idx_c, idx_x, idx_y) = match (idx_c, idx_x, idx_y) {
-            (Some(idx_c), Some(idx_x), Some(idx_y)) => (idx_c, idx_x, idx_y),
-            _ => return None,
+        let (Some(idx_c), Some(idx_x), Some(idx_y)) = (idx_c, idx_x, idx_y) else {
+            return None;
         };
 
         Some(0usize)

tests/reference_images.rs

@@ -267,9 +267,8 @@ fn check_references() {
             }
         }
 
-        let test_img = match test_img.as_ref() {
-            Some(img) => img,
-            None => return,
+        let Some(test_img) = test_img.as_ref() else {
+            return;
         };
 
         let test_crc_actual = {