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Nullable types — ColligoNullable

Colligo defines ColligoNullable<T> in Colligo.Core — a generic record that wraps any value type with a HasValue flag, similar to C# Nullable<T>.

Type aliases​

type
  NullableInt32    = ColligoNullable<Int32>;
  NullableInt64    = ColligoNullable<Int64>;
  NullableSingle   = ColligoNullable<Single>;
  NullableCurrency = ColligoNullable<Currency>;
  NullableDouble   = ColligoNullable<Double>;

Creating nullable values​

uses Colligo.Core;

var LValue: NullableInt32;

// With a value:
LValue := NullableInt32.Create(42);
Writeln(LValue.HasValue); // True
Writeln(LValue.Value);    // 42

// Empty:
LValue := NullableInt32.CreateEmpty;
Writeln(LValue.HasValue); // False
// LValue.Value → raises EInvalidOperation

Implicit conversion​

var LValue: NullableInt32 := 100; // implicit from Int32
var LRaw: Int32 := LValue;        // implicit to Int32 (raises if HasValue = False)

Equality​

var LA: NullableInt32 := 5;
var LB: NullableInt32 := 5;
if LA = LB then ...  // True — both have value 5

Use with aggregation operators​

Several Sum, Average, Min, Max overloads on IColligoEnumerable<T> accept nullable selectors. They skip elements where HasValue = False:

type TItem = record Price: NullableDouble; end;

var LTotal := TColligoArray<TItem>.From(LItems)
  .Sum(function(const I: TItem): NullableDouble begin Result := I.Price end);
// Skips items where Price.HasValue = False
// Raises EInvalidOperation if all items have HasValue = False
Empty sequence behaviour

Nullable aggregations raise EInvalidOperation when no element has a value. Use a Where filter before aggregating if the empty case is possible.