Question 4: .. in a tuple expression and pattern

questions/004-dotdot-in-tuple.md

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+Answer: 54
+Difficulty: 1
+
+# Hint
+
+`..` means one thing in an expression and something else in a pattern.
+
+# Explanation
+
+This question demonstrates two different meanings of `..`.
+
+In expression position, `..` is the syntax for constructing various types of
+ranges. Here the expression `(0, 1, ..)` is a tuple with three elements, the
+third one having type [`RangeFull`].
+
+[`RangeFull`]: https://doc.rust-lang.org/std/ops/struct.RangeFull.html
+
+On the other hand in a pattern, `..` is used to mean "any number of elements".
+So the pattern `(.., x, y)` matches a tuple with 2 or more elements, binding the
+second-last one to `x` and the last one to `y`.
+
+Coming out of the first line of `main`, we have `x = 1` and `y = (..)`. Thus the
+value printed is going to be `b"066"[..][1]`.
+
+The expression `b"066"` is a byte-string literal of type `&'static [u8; 3]`
+containing the three ASCII bytes `b'0'`, `b'6'`, `b'6'`.
+
+When we slice the byte-string with `RangeFull` we get a dynamically sized slice
+`[u8]` of length 3. Next we access element `1` of the slice, which is the byte
+`b'6'` of type `u8`. When printed, we see the decimal representation of the byte
+value of the ASCII digit 6, which is the number 54.

questions/004-dotdot-in-tuple.rs

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+fn main() {
+    let (.., x, y) = (0, 1, ..);
+    print!("{}", b"066"[y][x]);
+}