Avoiding a “Methods cannot be marked transient” compilation error

I recently needed to make an SObject field transient in a series of Apex wrapper objects used in a controller for a sequence of Visualforce wizard pages. Why is a whole other story.

Here is a simplified example of one of the wrappers:

public class ActionWrapper {
    public Action__c sob { get; private set; }
    public ActionWrapper(Action__c sob) {
        this.sob = sob;
    }
    // ...
}

Given the large amount of code that depended on these objects I wanted to hide the fact that the SObject field would be null each time a wizard page was posted and so tried code of this pattern (though with the SOQL done in bulk not in each get):

public class ActionWrapper {
    public transient Action__c sob {
        get {
            if (sob == null && sobId != null) {
                sob = [select ... from Action__c where Id = :sobId];
            }
            return sob;
        }
        private set {
            sob = value;
            sobId = sob.Id;
        }
    }
    private Id sobId;
    public ActionWrapper(Action__c sob) {
        this.sob = sob;
    }
    // ...
}

But this yields the error “Methods cannot be marked transient”: it looks like compilation of get or set without a body is handled differently from get or set with a body. Pretty discouraging…

The good news is that the following pattern solves the problem by separating the transient declaration from the get and set methods:

public class ActionWrapper {
    public Action__c sob {
        get {
            if (sobValue == null && sobId != null) {
                sobValue = [select ... from Action__c where Id = :sobId];
            }
            return sobValue;
        }
        private set {
            sobValue = value;
            sobId = sobValue.Id;
        }
    }
    private Id sobId;
    private transient Action__c sobValue;
    public ActionWrapper(Action__c sob) {
        this.sob = sob;
    }
    // ...
}