public void From_nullable_produces_correct_value_object(int?value, bool expectedHasValue)
{
var sut = Possible.From(value);
Assert.Equal(expectedHasValue, sut.HasValue);
if (sut.HasValue)
{
Assert.Equal(value.Value, sut.GetValue(-1));
}
}
static void Main(string[] args)
{
// One can convert any object ot IPossible<T>
var possibleIntViaStaticMethod = Possible.From(1);
var possibleIntViaExtensionsMethod = 1.ToPossible();
// That way, when an object contains null,
// and you wouldn't know it beforehand
// the Possible class will take that into account for you:
int? nullableInt = null;
var possibleIntFromNullableViaStaticMethod = Possible.From(nullableInt);
var posibleIntFromNullableViaExtensionMethod = nullableInt.ToPossible();
object @object = null;
var possibleObjectViaStaticMethod = Possible.From(@object);
var possibleObjectViaExtensionMethod = @object.ToPossible();
// You can pass in an optional lambda to determine whether an object is null or not,
// used below is the default expression when you pass no lambda
// which just checks whether the object is not null, then Possible.From
// assumes you have a value by "convention":
possibleObjectViaStaticMethod = Possible.From(@object, o => o != null);
possibleObjectViaExtensionMethod = @object.ToPossible(o => o != null);
// For string objects you can define a parsing strategy,
// the default one is StringValueParserStrategy.NullEmptyOrWhitespaceIsNoValue
// which translates to String.IsNullOrWhiteSpace()
var possibleStringViaStaticMethod = Possible.From(" ");
var possibleStringViaExtensionMethod = " ".ToPossible();
possibleStringViaStaticMethod = Possible.From(" ", StringValueParserStrategy.NullOrEmptyIsNoValue);
possibleStringViaExtensionMethod = " ".ToPossible(StringValueParserStrategy.NullOrEmptyIsNoValue);
// Given a possible object, one can get the original value back,
// but since you have no idea whether it contains a value or not,
// you are always obliged to pass in either a fixed default value
// or a function the produces a default value
var possible = "".ToPossible();
var real = possible.GetValue(""); // pass in a fixed value as the default
real = possible.GetValue(() => String.Empty); // pass in a function the produces a default value
// One can also check via a boolean property whether a possible
// has a value or not. But to avoid if-else branching in the code
// too much, we'd advice to use this as a last resort
var hasValue = possible.HasValue;
// Better is to use the methods Execute or Map
// - Execute will perform an action on the value when it is present
possible.Execute(value => Console.WriteLine(value));
// - Map will perform a function on the value if it is present,
// and produce a new possible result.
var newPossibleResult = possible.Map(value => value.Length);
// Extension methods provide options to be more flexible with
// collections of possible types
var collectionOfPossibleInts = new[] { -2, -1, 0, 1, 2, 3, 4, 5 }.Select(i => i.ToPossible());
// - SelectElementsWithValue will only return the elements with a value
var sumOfelementsWithValue = collectionOfPossibleInts
.SelectElementsWithValue()
.Sum();
// - MapElementsWithValue will only operate a mapping function on elements with a value
// and return back a collection of concrete results.
// Hence why you have to return a "possible" result in the function, so that
// the mapping function can automatically apply the SelectElementsWithValue
// method on it.
var mappedElementsWithValue = collectionOfPossibleInts
.MapElementsWithValue(i => i.ToString().ToPossible());
// - FirstOrNoValue is the replacement for Linq's FirstOrDefault
var firstOrNoValueResult = collectionOfPossibleInts
.FirstOrNoValue();
// - Where is the replacement for Linq'q Where
var intsLargerOrEqualThanZeroAsString = String.Join(", ",
collectionOfPossibleInts
.Where(i => i >= 0)
.SelectElementsWithValue()
.ToList()
);
Console.WriteLine($"{intsLargerOrEqualThanZeroAsString}.");
Console.ReadLine();
}
public static IPossible <TConcrete> ToPossible <TConcrete>(this TConcrete?value)
where TConcrete : struct
=> Possible.From(value);
public void From_string_produces_correct_value_object(string value, bool expectedHasValue, StringValueParserStrategy stringValueParserStrategy)
{
var sut = Possible.From(value, stringValueParserStrategy);
Assert.Equal(expectedHasValue, sut.HasValue);
}
public void From_produces_correct_value_object(object value, bool expectedHasValue, Func <object, bool> hasValueDeterminator)
{
var sut = Possible.From(value, hasValueDeterminator);
Assert.Equal(expectedHasValue, sut.HasValue);
}
public static IPossible <string> ToPossible(
this string value,
StringValueParserStrategy stringValueParserStrategy = StringValueParserStrategy.NullEmptyOrWhitespaceIsNoValue
) => Possible.From(value, stringValueParserStrategy);