List<Thing> things = makeThings();
foreach(var thing in things){
    thing = otherThing; // Fail
    thing.foo = bar; // Works as expected
}

if (slot.SlotRectangle.Contains(mousePosition) && slot.IsSlotOpen == false)
                    {
                        Item itemToDrop = new Item();

Shader modelVertexShader = new Shader(ShaderType.VertexShader);
Shader modelFragmentShader = new Shader(ShaderType.FragmentShader);

using (StreamReader r = new StreamReader("Assets/Shaders/Model.vert"))
{
    modelVertexShader.ShaderSource(r.ReadToEnd());
}

using (StreamReader r = new StreamReader("Assets/Shaders/Model.frag"))
{
    modelFragmentShader.ShaderSource(r.ReadToEnd());
}

modelShader = new ShaderProgram("Model");
modelShader.AttachShader(modelVertexShader);
modelShader.AttachShader(modelFragmentShader);

public class Mesh
{
    // GL Names
    int vao = 0, vertVbo = 0, normVbo = 0, tangentsVbo = 0, binormalsVbo = 0, uvVbo = 0, colorsVbo, ebo = 0;

    #region MeshData
    Vector3[] verts;
    Vector3[] norms;
    Vector3[] tangents;
    Vector3[] binormals;
    Vector3[] uv;
    Vector4[] colors;
    int[] indices;
    #endregion

    // Upload() will send "dirty" buffers to the GPU, and Draw() will just issue a draw command for the VAO
}

from the Upload():
if (colorsDirty && colors != null)
{
    colorsDirty = false;

    if (colorsVbo == 0) GL.GenBuffers(1, out colorsVbo);

    UploadData(colorsVbo, BufferTarget.ArrayBuffer, colors.Length * Vector4.SizeInBytes, colors);
}