// generate Copy lambda based on passed-in type
static void Copy(IUntypedField field, IFieldMap from, IFieldMap to)
{
// figure out what type we need to look up;
// we know we have a Field<TValue>, so find TValue
Type type = field.GetType().GetGenericArguments()[0];
Action <IUntypedField, IFieldMap, IFieldMap> copier;
if (!copiers.TryGetValue(type, out copier))
{
// copier not found; create a lambda and compile it
Type tFieldMap = typeof(IFieldMap);
// create parameters to lambda
ParameterExpression
fieldParam = Expression.Parameter(typeof(IUntypedField)),
fromParam = Expression.Parameter(tFieldMap),
toParam = Expression.Parameter(tFieldMap);
// create expression for "(Field<TValue>)field"
var converter = Expression.Convert(fieldParam, field.GetType());
// create expression for "to.Put(field, from.Get(field))"
var copierExp =
Expression.Call(
toParam,
tFieldMap.GetMethod("Put").MakeGenericMethod(type),
converter,
Expression.Call(
fromParam,
tFieldMap.GetMethod("Get").MakeGenericMethod(type),
converter));
// create our lambda and compile it
copier =
Expression.Lambda <Action <IUntypedField, IFieldMap, IFieldMap> >(
copierExp,
fieldParam,
fromParam,
toParam)
.Compile();
// add the compiled lambda to the cache
copiers[type] = copier;
}
// invoke the actual copy lambda
copier(field, from, to);
}
// non-generic overload of Copy
void Copy(IUntypedField field, IFieldMap from, IFieldMap to)
{
to.PutObject(field, from.GetObject(field));
}
