Add Circular Buffer solution

Author: blogscot

circular-buffer/.gitignore

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+# Generated by Cargo
+# will have compiled files and executables
+/target/
+**/*.rs.bk
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
+Cargo.lock

circular-buffer/Cargo.toml

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+[package]
+name = "circular-buffer"
+version = "0.0.0"

circular-buffer/README.md

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+# Circular Buffer
+
+A circular buffer, cyclic buffer or ring buffer is a data structure that
+uses a single, fixed-size buffer as if it were connected end-to-end.
+
+A circular buffer first starts empty and of some predefined length. For
+example, this is a 7-element buffer:
+
+    [ ][ ][ ][ ][ ][ ][ ]
+
+Assume that a 1 is written into the middle of the buffer (exact starting
+location does not matter in a circular buffer):
+
+    [ ][ ][ ][1][ ][ ][ ]
+
+Then assume that two more elements are added — 2 & 3 — which get
+appended after the 1:
+
+    [ ][ ][ ][1][2][3][ ]
+
+If two elements are then removed from the buffer, the oldest values
+inside the buffer are removed. The two elements removed, in this case,
+are 1 & 2, leaving the buffer with just a 3:
+
+    [ ][ ][ ][ ][ ][3][ ]
+
+If the buffer has 7 elements then it is completely full:
+
+    [6][7][8][9][3][4][5]
+
+When the buffer is full an error will be raised, alerting the client
+that further writes are blocked until a slot becomes free.
+
+When the buffer is full, the client can opt to overwrite the oldest
+data with a forced write. In this case, two more elements — A & B —
+are added and they overwrite the 3 & 4:
+
+    [6][7][8][9][A][B][5]
+
+3 & 4 have been replaced by A & B making 5 now the oldest data in the
+buffer. Finally, if two elements are removed then what would be
+returned is 5 & 6 yielding the buffer:
+
+    [ ][7][8][9][A][B][ ]
+
+Because there is space available, if the client again uses overwrite
+to store C & D then the space where 5 & 6 were stored previously will
+be used not the location of 7 & 8. 7 is still the oldest element and
+the buffer is once again full.
+
+    [D][7][8][9][A][B][C]
+
+## Rust Installation
+
+Refer to the [exercism help page][help-page] for Rust installation and learning
+resources.
+
+## Writing the Code
+
+Execute the tests with:
+
+```bash
+$ cargo test
+```
+
+All but the first test have been ignored. After you get the first test to
+pass, open the tests source file which is located in the `tests` directory
+and remove the `#[ignore]` flag from the next test and get the tests to pass
+again. Each separate test is a function with `#[test]` flag above it.
+Continue, until you pass every test. 
+
+If you wish to run all tests without editing the tests source file, use:
+
+```bash
+$ cargo test -- --ignored
+```
+
+To run a specific test, for example `some_test`, you can use:
+
+```bash
+$ cargo test some_test
+```
+
+If the specific test is ignored use:
+
+```bash
+$ cargo test some_test -- --ignored
+```
+
+To learn more about Rust tests refer to the [online test documentation][rust-tests]
+
+Make sure to read the [Modules](https://doc.rust-lang.org/book/second-edition/ch07-00-modules.html) chapter if you
+haven't already, it will help you with organizing your files.
+
+## Feedback, Issues, Pull Requests
+
+The [exercism/rust](https://github.com/exercism/rust) repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!
+
+If you want to know more about Exercism, take a look at the [contribution guide](https://github.com/exercism/docs/blob/master/contributing-to-language-tracks/README.md).
+
+[help-page]: http://exercism.io/languages/rust
+[modules]: https://doc.rust-lang.org/book/second-edition/ch07-00-modules.html
+[cargo]: https://doc.rust-lang.org/book/second-edition/ch14-00-more-about-cargo.html
+[rust-tests]: https://doc.rust-lang.org/book/second-edition/ch11-02-running-tests.html
+
+## Source
+
+Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

circular-buffer/src/lib.rs

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+use std::collections::VecDeque;
+
+#[derive(Debug, PartialEq)]
+pub enum Error {
+  EmptyBuffer,
+  FullBuffer,
+}
+
+pub struct CircularBuffer<T> {
+  size: usize,
+  buffer: VecDeque<T>,
+}
+
+impl<T> CircularBuffer<T> {
+  pub fn new(size: usize) -> Self {
+    CircularBuffer {
+      size,
+      buffer: VecDeque::with_capacity(size),
+    }
+  }
+  fn is_buffer_full(&self) -> bool {
+    self.buffer.len() >= self.size
+  }
+  pub fn read(&mut self) -> Result<T, Error> {
+    self.buffer.pop_front().ok_or(Error::EmptyBuffer)
+  }
+  pub fn write(&mut self, value: T) -> Result<(), Error> {
+    if self.is_buffer_full() {
+      return Err(Error::FullBuffer);
+    }
+    self.buffer.push_back(value);
+    Ok(())
+  }
+  pub fn clear(&mut self) {
+    self.buffer.clear();
+  }
+  pub fn overwrite(&mut self, value: T) {
+    if self.is_buffer_full() {
+      self.buffer.pop_front();
+    }
+    self.buffer.push_back(value);
+  }
+}

circular-buffer/tests/circular-buffer.rs

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+extern crate circular_buffer;
+use circular_buffer::{CircularBuffer, Error};
+
+#[test]
+fn error_on_read_empty_buffer() {
+    let mut buffer = CircularBuffer::<char>::new(1);
+    assert_eq!(Err(Error::EmptyBuffer), buffer.read());
+}
+
+#[test]
+fn write_and_read_back_item() {
+    let mut buffer = CircularBuffer::new(1);
+    assert!(buffer.write('1').is_ok());
+    assert_eq!(Ok('1'), buffer.read());
+    assert_eq!(Err(Error::EmptyBuffer), buffer.read());
+}
+
+#[test]
+fn write_and_read_back_multiple_items() {
+    let mut buffer = CircularBuffer::new(2);
+    assert!(buffer.write('1').is_ok());
+    assert!(buffer.write('2').is_ok());
+    assert_eq!(Ok('1'), buffer.read());
+    assert_eq!(Ok('2'), buffer.read());
+    assert_eq!(Err(Error::EmptyBuffer), buffer.read());
+}
+
+#[test]
+fn alternate_write_and_read() {
+    let mut buffer = CircularBuffer::new(2);
+    assert!(buffer.write('1').is_ok());
+    assert_eq!(Ok('1'), buffer.read());
+    assert!(buffer.write('2').is_ok());
+    assert_eq!(Ok('2'), buffer.read());
+}
+
+#[test]
+fn clear_buffer() {
+    let mut buffer = CircularBuffer::new(3);
+    assert!(buffer.write('1').is_ok());
+    assert!(buffer.write('2').is_ok());
+    assert!(buffer.write('3').is_ok());
+    buffer.clear();
+    assert_eq!(Err(Error::EmptyBuffer), buffer.read());
+    assert!(buffer.write('1').is_ok());
+    assert!(buffer.write('2').is_ok());
+    assert_eq!(Ok('1'), buffer.read());
+    assert!(buffer.write('3').is_ok());
+    assert_eq!(Ok('2'), buffer.read());
+}
+
+#[test]
+fn full_buffer_error() {
+    let mut buffer = CircularBuffer::new(2);
+    assert!(buffer.write('1').is_ok());
+    assert!(buffer.write('2').is_ok());
+    assert_eq!(Err(Error::FullBuffer), buffer.write('3'));
+}
+
+#[test]
+fn overwrite_item_in_non_full_buffer() {
+    let mut buffer = CircularBuffer::new(2);
+    assert!(buffer.write('1').is_ok());
+    buffer.overwrite('2');
+    assert_eq!(Ok('1'), buffer.read());
+    assert_eq!(Ok('2'), buffer.read());
+    assert_eq!(Err(Error::EmptyBuffer), buffer.read());
+}
+
+#[test]
+fn overwrite_item_in_full_buffer() {
+    let mut buffer = CircularBuffer::new(2);
+    assert!(buffer.write('1').is_ok());
+    assert!(buffer.write('2').is_ok());
+    buffer.overwrite('A');
+    assert_eq!(Ok('2'), buffer.read());
+    assert_eq!(Ok('A'), buffer.read());
+}
+
+#[test]
+fn integer_buffer() {
+    let mut buffer = CircularBuffer::new(2);
+    assert!(buffer.write(1).is_ok());
+    assert!(buffer.write(2).is_ok());
+    assert_eq!(Ok(1), buffer.read());
+    assert!(buffer.write(-1).is_ok());
+    assert_eq!(Ok(2), buffer.read());
+    assert_eq!(Ok(-1), buffer.read());
+    assert_eq!(Err(Error::EmptyBuffer), buffer.read());
+}
+
+#[test]
+fn string_buffer() {
+    let mut buffer = CircularBuffer::new(2);
+    buffer.write("".to_string()).unwrap();
+    buffer.write("Testing".to_string()).unwrap();
+    assert_eq!(0, buffer.read().unwrap().len());
+    assert_eq!(Ok("Testing".to_string()), buffer.read());
+}