R. v. Parker, 2013 ONCJ 195 deals with recent amendments to the law of self-defence in Canada. It asks does the new law apply to assist an accused where the crime alleged took place before the change in the law? The Court holds the new law (and the earlier law also) applies:
 With respect, I have reservations about this outcome. Parliament has declared, through the passage of section 34, what level of force contemporary Canadian society now considers justifiable. A justification, such as self-defence, "challenges the wrongfulness of an action which technically constitutes a crime" and exists because "the concept of punishment often seems incompatible with the social approval bestowed on the doer": R. v. Perka1984 CanLII 23 (SCC),  2 S.C.R. 232. There is, in my view, no public interest in convicting someone of an act that is considered and declared by Parliament by the time of trial to have social approval and not to be wrong, even if that declaration occurred after the event in question. It is important to remember that the principles against retroactivity that have long applied in criminal cases are related to the Rule of Law. They were intended to protect individuals from abusive state powers. These principles have been embraced, according to Bentham, "in the true spirit of liberty." Jeremy Bentham, 1 Works 326 (Bowring ed. 1843) cited in Jerome Hall, General Principles of Criminal Law (2d ed), (Indianapolis: The Bobbs-Merrill Company Inc., 1960). Since defences are used in criminal cases to prevent deprivations of liberty, the foundational rationale for non-retroactivity is in my view undermined when it comes to new defences. To put things more simply, it would defeat the objectives of the presumption against retroactivity to apply it to new defences in criminal cases and it would result in actions, considered justifiable and legal at the time of trial, to be condemned and punished by conviction. The Charter, of course, is silent on this issue, but it does provide in section 11(i) that accused persons receive the benefit of subsequently enacted, more generous sentencing regimes. Although this provision does not address changes in defences, the values it reflects are indistinguishable from the principle I am describing; accused persons should receive the benefit of the law in place at the time of their alleged offence, as well as the benefit of new substantive provisions in effect at the time of their trials that protect their liberty interests. In my view, there is no realistic basis for presuming in such cases that Parliament must have intended to apply those rules only in the future. Instead, Parliament can and should be taken to intend that when a new defence is created, accused persons yet to be tried for previous alleged offences should have access to that defence where it operates more generously for them than the prior law. For this reason I will consider both defences in this case, now repealed subsection 34(2) and the current defence of self-defence now found in section 34.