In Frost v Knight, the defendant had promised that when the plaintiff’s father died, he would marry her. However, during the father’s lifetime, the defendant broke off his engagement to the plaintiff. Without waiting for the death of her father, the plaintiff sued immediately for breach of promise of marriage:

Frost v Knight (1872) LR 7 Exch 111, p 112 Cockburn CJ: The law with reference to a contract to be performed at a future time, where the party bound to performance announces prior to the time his intention not to perform it, as established by the cases of Hochster v De La Tour and The Danube and Black Sea Co v Xenos on the one hand, and Avery v Bowden, Reid v Hoskins and Barwick v Buba on the other, may be thus stated. The promisee, if he pleases, may treat the notice of intention as inoperative, and await the time when the contract is to be executed, and then hold the other party responsible for all the consequences of non-performance: but in that case he keeps the contract alive for the benefit of the other party as well as his own; he remains subject to all his own obligations and liabilities under it, and enables the other party not only to complete the contract, if so advised, notwithstanding his previous repudiation of it, but also to take advantage of any supervening circumstance which would justify him in declining to complete it.