feat(buffer): new api from_{bytes, array, iter}

Author: jetjinser

buffer/buffer.mbt

@@ -162,6 +162,30 @@ pub fn new(size_hint~ : Int = 0) -> T {
   { data, len: 0, initial_data: data }
 }
 
+///| Create a buffer from a bytes.
+pub fn T::from_bytes(bytes : Bytes) -> T {
+  let buf = T::new(size_hint=bytes.length())
+  buf.write_bytes(bytes)
+  buf
+}
+
+///|
+/// Create a buffer from an array.
+pub fn T::from_array(arr : Array[Byte]) -> T {
+  let buf = T::new(size_hint=arr.length())
+  for byte in arr {
+    buf.write_byte(byte)
+  }
+  buf
+}
+
+///|
+/// Create a buffer from an array.
+pub fn T::from_iter(iter : Iter[Byte]) -> T {
+  let arr = iter.collect()
+  T::from_array(arr)
+}
+
 ///|
 /// Writes a UTF-16LE encoded string into the buffer. The buffer will
 /// automatically grow if needed to accommodate the string.

buffer/buffer.mbti

@@ -7,6 +7,9 @@ fn new(size_hint~ : Int = ..) -> T
 type T
 impl T {
   contents(Self) -> Bytes
+  from_array(Array[Byte]) -> Self
+  from_bytes(Bytes) -> Self
+  from_iter(Iter[Byte]) -> Self
   is_empty(Self) -> Bool
   length(Self) -> Int
   new(size_hint~ : Int = ..) -> Self //deprecated

buffer/buffer_test.mbt

@@ -12,6 +12,24 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+test "create buffer from bytes" {
+  let bytes = b"1\x002\x003\x00"
+  let buf = @buffer.from_bytes(bytes)
+  inspect!(buf, content="123")
+}
+
+test "create buffer from array" {
+  let arr = [b'4', b'\x00', b'5', b'\x00', b'6', b'\x00']
+  let buf = @buffer.from_array(arr)
+  inspect!(buf, content="456")
+}
+
+test "create buffer from iterator" {
+  let iter = [b'5', b'\x00', b'6', b'\x00', b'7', b'\x00'].iter()
+  let buf = @buffer.from_iter(iter)
+  inspect!(buf, content="567")
+}
+
 test "length method" {
   let buf = @buffer.new(size_hint=100)
   inspect!(buf.length(), content="0")