What is the test for determining whether a statute has retrospective effect?

In Elliott v. City of Saskatoon[10], Mr. Justice Gerein concluded that, when considering whether a statute has retrospective operation, one must consider two classes of cases – those where the new statute affects existing substantive rights and those where it affects only the existing practice and procedure for enforcing those rights. After considering the authorities, Justice Gerein formulated five principles as follows: 1. Legislation which is only procedural is to be construed as retrospective. 2. Legislation which affects substantive or vested rights is to be construed as prospective; 3. Legislation which is procedural, but which also affects substantive or vested rights, is to be construed as prospective; 4. Legislation which impairs substantive or vested rights should be given retrospective effect if the legislature has clearly expressed such an intention. 5. A statutory defence is a substantive and vested right.