Add format function and test for it (#13)

feat: add format function

src/deque.zig

@@ -160,6 +160,24 @@ pub fn Deque(comptime T: type) type {
  };
  }
 
+ pub fn format(self: *const Self, comptime _: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+ try writer.writeAll("Deque(");
+ try std.fmt.format(writer, "{}", .{T});
+ try writer.writeAll(") { .buf = [");
+
+ var it = self.iterator();
+ if (it.next()) |val| try writer.print("{any}", .{val});
+ while (it.next()) |val| try writer.print(", {any}", .{val});
+
+ try writer.writeAll("], .head = ");
+ try std.fmt.format(writer, "{}", .{self.head});
+ try writer.writeAll(", .tail = ");
+ try std.fmt.format(writer, "{}", .{self.tail});
+ try writer.writeAll(", .len = ");
+ try std.fmt.format(writer, "{}", .{self.len()});
+ try writer.writeAll(" }");
+ }
+
  pub const Iterator = struct {
  head: usize,
  tail: usize,
@@ -373,6 +391,18 @@ test "appendSlice and prependSlice" {
  }
 }
 
+test "format" {
+ const testing = std.testing;
+
+ var deque = try Deque(usize).init(testing.allocator);
+ defer deque.deinit();
+
+ try deque.pushBack(69);
+ try deque.pushBack(420);
+
+ std.debug.print("{}\n", .{deque});
+}
+
 test "nextBack" {
  const testing = std.testing;