public ComparerBuilder <TItem> Compare <TField>(Func <TItem, TField> expression, IComparer <TField> comparer, OrderFlavour flavour = OrderFlavour.Default)
{
if (expression == null)
{
throw new ArgumentNullException("expression");
}
if (comparer == null)
{
throw new ArgumentNullException("comparer");
}
Func <object, object, int> fieldComparison = delegate(object x, object y)
{
var f = flavour; // stack is faster then heap
bool areNullsEarly = (f & OrderFlavour.NullGoesEarly) != 0;
bool isBackward = (f & OrderFlavour.Backward) != 0;
// 1. x & y are unconditionally NOT NULL and type of them is defenitely TItem
// 2. The compiler replaces null comparisons with a call to HasValue for nullable types
TField xField = expression((TItem)x);
TField yField = expression((TItem)y);
if (TypeInfo <TField> .IsReferenceType && ReferenceEquals(xField, yField))
{
return(0);
}
if (xField == null && yField == null)
{
return(0);
}
if (xField == null)
{
return(areNullsEarly ? -1 : 1);
}
if (yField == null)
{
return(areNullsEarly ? 1 : -1);
}
int ret = comparer.Compare(xField, yField);
return(isBackward ? -ret : ret);
};
_Comparisons.Add(new FieldMeta()
{
Comparison = fieldComparison,
});
return(this);
}
public Comparison <TItem> GetComparison(OrderFlavour flavour = OrderFlavour.Default)
{
// ThreadSafe
return(new ItemComparer <TItem>(_Comparisons, OrderFlavour.Default).Compare);
}
public IComparer <TItem> GetComparer(OrderFlavour flavour = OrderFlavour.Default)
{
return(new ItemComparer <TItem>(_Comparisons, flavour));
}
public ComparerBuilder <TItem> CompareString(Func <TItem, string> expression, StringComparer comparer, OrderFlavour flavour = OrderFlavour.Default)
{
return(Compare(expression, comparer, flavour));
}
public ComparerBuilder <TItem> Compare <TField>(Func <TItem, TField> expression, OrderFlavour flavour = OrderFlavour.Default)
{
return(Compare(expression, Comparer <TField> .Default, flavour));
}
public ItemComparer(List <FieldMeta> fields, OrderFlavour orderFlavour)
{
_Fields = fields;
_OrderFlavour = orderFlavour;
}
