Add Piece::spawn() function, Spawn trait

mino/src/piece.rs

@@ -15,6 +15,13 @@ pub struct Loc {
     pub r: Rot,
 }
 
+impl From<(i16, i16)> for Loc {
+    fn from((x, y): (i16, i16)) -> Self {
+        let r = Rot::default();
+        Loc { x, y, r }
+    }
+}
+
 /// Represents a rotation state for a piece. The initial state is "north" (`N`), and there
 /// are 4 total orientations to represent each 90 degree turn possible.
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Default)]
@@ -165,6 +172,19 @@ impl<'c, S: Shape<'c>> Piece<S> {
     }
 }
 
+/// Interface for piece types that have a initial spawn location.
+pub trait Spawn {
+    /// Returns the (x,y) coordinates where the piece should spawn.
+    fn spawn_pos(&self) -> (i16, i16);
+}
+
+impl<S: Spawn> Piece<S> {
+    pub fn spawn(shape: S) -> Self {
+        let loc = shape.spawn_pos().into();
+        Self { shape, loc }
+    }
+}
+
 #[cfg(test)]
 pub mod test {
     use super::*;