j5ik2o · August 14, 2020 08:32 · Aug 14, 2020
diff --git a/ToyVec.rs b/ToyVec.rs
@@ -0,0 +1,140 @@
+pub struct ToyVec<T> {
+    elements: Box<[T]>,
+    len: usize,
+}
+
+pub struct Iter<'vec, T> {
+    // 参照型のフィールドにはライフタイム指定子
+    elements: &'vec Box<[T]>,
+    len: usize,
+    pos: usize,
+}
+
+impl<'vec, T> Iterator for Iter<'vec, T> {
+    type Item = &'vec T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.pos >= self.len {
+            None
+        } else {
+            let res = Some(&self.elements[self.pos]);
+            self.pos += 1;
+            res
+        }
+    }
+}
+
+impl<'vec, T: Default> IntoIterator for &'vec ToyVec<T> {
+    type Item = &'vec T;
+    type IntoIter = Iter<'vec, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+
+impl<T: Default> ToyVec<T> {
+    pub fn iter<'vec>(&'vec self) -> Iter<'vec, T> {
+        Iter {
+            elements: &self.elements,
+            len: self.len,
+            pos: 0
+        }
+    }
+    pub fn new() -> Self {
+        Self::with_capacity(0)
+    }
+
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            elements: Self::allocate_in_heap(capacity),
+            len: 0,
+        }
+    }
+
+    fn allocate_in_heap(size: usize) -> Box<[T]> {
+        std::iter::repeat_with(Default::default)
+            .take(size)
+            .collect::<Vec<_>>()
+            .into_boxed_slice()
+    }
+
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    pub fn capacity(&self) -> usize {
+        self.elements.len()
+    }
+
+    pub fn push(&mut self, element: T) {
+        if self.len == self.capacity() {
+            self.grow();
+        }
+        self.elements[self.len] = element;
+        self.len += 1;
+    }
+
+    pub fn get(&self, index: usize) -> Option<&T> {
+        if index < self.len {
+            Some(&self.elements[index])
+        } else {
+            None
+        }
+    }
+
+    pub fn get_or<'a, 'b>(&'a self, index: usize, default: &'b T) -> &'a T
+        where
+            'b: 'a
+    {
+        self.get(index).unwrap_or(default)
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        if self.len == 0 {
+            None
+        } else {
+            self.len -= 1;
+            let elm = std::mem::replace(&mut self.elements[self.len], Default::default());
+            Some(elm)
+        }
+    }
+
+    // pub fn take(&mut self) -> Option<T> {
+    //
+    // }
+    //
+    // pub fn replace(&mut self, value: T)-> Option<T> {
+    //
+    // }
+
+    fn grow(&mut self) {
+        if self.capacity() == 0 {
+            self.elements = Self::allocate_in_heap(1);
+        } else {
+            let new_elements = Self::allocate_in_heap(self.capacity() * 2);
+            // 新しい要素をself.elementsに置き換える。この時点で2倍の要素数になる
+            let old_elements = std::mem::replace(&mut self.elements, new_elements);
+            // into_iterでムーブする
+            for (i, elm) in old_elements.into_vec().into_iter().enumerate() {
+                self.elements[i] = elm;
+            }
+        }
+    }
+}
+
+fn main() {
+    let mut v = ToyVec::new();
+    v.push("Java Finch".to_string());
+    v.push("Budgerigar".to_string());
+    let mut iter = v.iter();
+    iter.next();
+    iter.next();
+    let a = iter.next();
+    println!("{:?}", a);
+    v.push("Budgerigar2".to_string());
+    // for msg in &v {
+    //     println!("{:?}", msg);
+    // }
+}
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