add defaults for the several structs

src/dynamics/joint/fixed_joint.rs

@@ -6,7 +6,11 @@ use crate::math::{Isometry, Point, Real};
 pub struct FixedJoint {
     data: JointData,
 }
-
+impl Default for FixedJoint{
+    fn default() -> Self {
+        FixedJoint::new()
+    }
+}
 impl FixedJoint {
     pub fn new() -> Self {
         #[cfg(feature = "dim2")]

src/dynamics/joint/multibody_joint/multibody.rs

@@ -18,7 +18,7 @@ use na::{
 };
 
 #[repr(C)]
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug,Default)]
 struct Force {
     linear: Vector<Real>,
     angular: AngVector<Real>,
@@ -91,7 +91,11 @@ pub struct Multibody {
     coriolis_w: Vec<OMatrix<Real, AngDim, Dynamic>>,
     i_coriolis_dt: Jacobian<Real>,
 }
-
+impl Default for Multibody{
+    fn default() -> Self {
+        Multibody::new()
+    }
+}
 impl Multibody {
     /// Creates a new multibody with no link.
     pub fn new() -> Self {

src/dynamics/joint/multibody_joint/multibody_joint_set.rs

@@ -75,6 +75,7 @@ impl Default for MultibodyJointLink {
     }
 }
 
+#[derive(Default)]
 /// A set of rigid bodies that can be handled by a physics pipeline.
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 #[derive(Clone)]

src/dynamics/joint/spherical_joint.rs

@@ -7,7 +7,11 @@ use crate::math::{Point, Real};
 pub struct SphericalJoint {
     data: JointData,
 }
-
+impl Default for SphericalJoint{
+    fn default() -> Self {
+        SphericalJoint::new()
+    }
+}
 impl SphericalJoint {
     pub fn new() -> Self {
         let data =

src/dynamics/rigid_body_components.rs

@@ -12,7 +12,7 @@ use crate::utils::{WAngularInertia, WCross, WDot};
 use num::Zero;
 
 /// The unique handle of a rigid body added to a `RigidBodySet`.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Default)]
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 #[repr(transparent)]
 pub struct RigidBodyHandle(pub crate::data::arena::Index);

src/dynamics/solver/delta_vel.rs

@@ -3,7 +3,7 @@ use na::{DVectorSlice, DVectorSliceMut};
 use na::{Scalar, SimdRealField};
 use std::ops::{AddAssign, Sub};
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Default)]
 #[repr(C)]
 //#[repr(align(64))]
 pub struct DeltaVel<N: Scalar + Copy> {

src/dynamics/solver/joint_constraint/joint_generic_velocity_constraint.rs

@@ -29,6 +29,12 @@ pub struct JointGenericVelocityConstraint {
     pub writeback_id: WritebackId,
 }
 
+impl Default for JointGenericVelocityConstraint {
+    fn default() -> Self {
+        JointGenericVelocityConstraint::invalid()
+    }
+}
+
 impl JointGenericVelocityConstraint {
     pub fn invalid() -> Self {
         Self {
@@ -313,6 +319,11 @@ pub struct JointGenericVelocityGroundConstraint {
 
     pub writeback_id: WritebackId,
 }
+impl Default for JointGenericVelocityGroundConstraint{
+    fn default() -> Self {
+        JointGenericVelocityGroundConstraint::invalid() 
+    }
+}
 
 impl JointGenericVelocityGroundConstraint {
     pub fn invalid() -> Self {