private ConstructedValueExpression AddInstantiationExpressionForObjectInstance(MapTypeContext context)
{
var instanceVar = context.CreateVariable(context.TargetType, "instance");
var typeInfo = context.Settings.GetTypeSettings(context.TargetType);
var defaultSubtypeInfo = typeInfo.GetDefault();
var defaultInstantiationExpression = AddInstantiationExpressionForSpecificType(context, defaultSubtypeInfo, instanceVar);
var subclasses = typeInfo.GetSpecificTypes().ToList();
// If we have no configured subclass predicates, instantiate the target type directly
if (subclasses.Count == 0)
{
return(new ConstructedValueExpression(defaultInstantiationExpression.Expressions, instanceVar, defaultInstantiationExpression.Variables.Concat(new[] { instanceVar })));
}
// If we have configured subclass predicates, unroll the loop and write expressions for
// all cases. The default case will be executed if no subclass predicates match.
var endLabel = context.CreateLabel("haveinstance");
var expressions = new List <Expression>();
foreach (var subclass in subclasses.Where(s => s.Predicate != null))
{
var instantiateExpressions = AddInstantiationExpressionForSpecificType(context, subclass, instanceVar);
// Check the subclass predicate. If it matches, we enter into a block where we
// create the subclass instance and then jump to the end label. Otherwise we
// fall through to the next subclass.
expressions.Add(
Expression.IfThen(
Expression.Call(
Expression.Constant(subclass.Predicate.Target),
subclass.Predicate.Method,
context.RecordParameter
),
Expression.Block(
instantiateExpressions.Variables,
instantiateExpressions.Expressions.Concat(new[] {
Expression.Goto(endLabel.Target)
})
)
)
);
}
// A block where we fall back to the default instantiation rules for the type, and then
// fall through to the endLabel. The block here allows us to scope variables a little
// more tightly
expressions.Add(
Expression.Block(
defaultInstantiationExpression.Variables,
defaultInstantiationExpression.Expressions
)
);
expressions.Add(endLabel);
return(new ConstructedValueExpression(expressions, instanceVar, new[] { instanceVar }));
}
