small spelling/grammar errors

[rust-101.git] / workspace / src / part09.rs

diff --git a/workspace/src/part09.rs b/workspace/src/part09.rs
index dc329bce3c2ad18f626ead094f5a6970a7e5d9e2..61cc70b8ddb6b678030b4f57892717668ad36d55 100644 (file)
--- a/workspace/src/part09.rs
+++ b/workspace/src/part09.rs
@@ -1,4 +1,85 @@
-// Rust-101, Part 09: Iterators (WIP)
-// =================================
+// Rust-101, Part 09: Iterators
+// ============================
+
+use part05::BigInt;
+
+
+pub struct Iter<'a> {
+    num: &'a BigInt,
+    idx: usize, // the index of the last number that was returned
+}
+
+// Now we are equipped to implement `Iterator` for `Iter`.
+impl<'a> Iterator for Iter<'a> {
+    // We choose the type of things that we iterate over to be the type of digits, i.e., `u64`.
+    type Item = u64;
+
+    fn next(&mut self) -> Option<u64> {
+        // First, check whether there's any more digits to return.
+        if self.idx == 0 {
+            // We already returned all the digits, nothing to do.
+            unimplemented!()
+        } else {
+            // Otherwise: Decrement, and return next digit.
+            unimplemented!()
+        }
+    }
+}
+
+// All we need now is a function that creates such an iterator for a given `BigInt`.
+impl BigInt {
+    fn iter(&self) -> Iter {
+        unimplemented!()
+    }
+}
+
+// We are finally ready to iterate! Remember to edit `main.rs` to run this function.
+pub fn main() {
+    let b = BigInt::new(1 << 63) + BigInt::new(1 << 16) + BigInt::new(1 << 63);
+    for digit in b.iter() {
+        println!("{}", digit);
+    }
+}
+
+// Of course, we don't have to use `for` to apply the iterator. We can also explicitly call `next`.
+fn print_digits_v1(b: &BigInt) {
+    let mut iter = b.iter();
+    loop {
+        // Each time we go through the loop, we analyze the next element presented by the iterator - until it stops.
+        unimplemented!()
+    }
+}
+
+fn print_digits_v2(b: &BigInt) {
+    let mut iter = b.iter();
+    while let Some(digit) = iter.next() {
+        println!("{}", digit)
+    }
+}
+
+// **Exercise 09.1**: Write a testcase for the iterator, making sure it yields the corrects numbers.
+// 
+// **Exercise 09.2**: Write a function `iter_ldf` that iterators over the digits with the least-significant
+// digits coming first. Write a testcase for it.
+
+// ## Iterator invalidation and lifetimes
+
+fn iter_invalidation_demo() {
+    let mut b = BigInt::new(1 << 63) + BigInt::new(1 << 16) + BigInt::new(1 << 63);
+    for digit in b.iter() {
+        println!("{}", digit);
+        /*b = b + BigInt::new(1);*/                                 /* BAD! */
+    }
+}
+
+// ## Iterator conversion trait
+
+impl<'a> IntoIterator for &'a BigInt {
+    type Item = u64;
+    type IntoIter = Iter<'a>;
+    fn into_iter(self) -> Iter<'a> {
+        self.iter()
+    }
+}
+// With this in place, you can now replace `b.iter()` in `main` by `&b`. Go ahead and try it! <br/>
 
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