In Johnson v. State of California (1968) 69 Cal. 2d 782, a government official placed a " '16 year old boy with homicidal tendencies' " in Mrs. Johnson's home as a foster child and failed to warn her of the child's " 'dangerous propensities,' " even though the placement officer had notice of the danger. After five days in Mrs. Johnson's home, the boy assaulted and injured her. (Id. at pp. 784-785.) Mrs. Johnson sued the state, alleging the state " 'should have told me I was getting a boy with a criminal and delinquent background.' " (Id. at p. 785, fn. 1.) The trial court granted summary judgment in favor of the state, on the ground the placement officer's decision whether to warn of the boy's potentially dangerous propensities was a "discretionary act" protected by section 820.2. (Johnson, at p. 786.) The Supreme Court reversed. In construing the scope of section 820.2 immunity, the court held "a semantic inquiry into the meaning of 'discretionary' will not suffice as a criterion for interpreting section 820.2." (Johnson, supra, 69 Cal. 2d at p. 787, ) The court instead analyzed the policy underlying a grant of immunity to determine what conduct should be protected by section 820.2. " 'Since obviously no mechanical separation of all activities in which public officials may engage as being either discretionary or ministerial is possible, the determination of the category into which a particular activity falls should be guided by the purpose of the discretionary immunity doctrine.' " (Johnson, 69 Cal. 2d at p. 790.)