Loyc.Maybe< T > Struct Template Reference

Same as Nullable{T} except that it behaves like a normal type, i.e. (1) T is allowed to be a reference type and (2) you can nest them, as in Maybe{Maybe{int}}. More...

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Source file:

• /Core/Loyc.Essentials/Utilities/Maybe.cs

Inheritance diagram for Loyc.Maybe< T >:

Remarks

Same as Nullable{T} except that it behaves like a normal type, i.e. (1) T is allowed to be a reference type and (2) you can nest them, as in Maybe{Maybe{int}}.

The name of this type comes from some functional programming languages which define a type such as data Maybe t = Nothing | Just t.

This type exists primarily for generic code, since C# does not allow you to write a generic function that returns "T?" if T could be a class. Places where this type is used include the DictionaryExt.TryGetValue(key) extension method, and the ILexer<T>.NextToken() method. Both of these may not be able to return a value, but they cannot return T? because T could be a class (or even a Nullable-of-something).

There is an implicit conversion from T that returns new Maybe{T}(value), and from NoValue.Value that returns Maybe{T}.NoValue. Since C# doesn't allow us to define conversions to/from T?, these conversions can be accomplished with the extension methods Maybe.AsNullable and Maybe.AsMaybe.

The Or method replicates the C# ?? operator.

Public fields
readonly T	_value
readonly bool	_hasValue

Properties
static Maybe< T >	NoValue [get]
bool	HasValue [get]
T	Value [get]
Properties inherited from Loyc.IHasValue< out T >
T	Value [get]

Public Member Functions
	Maybe (T value)
T	Or (T defaultValue)
	Converts Maybe{T} to T, returning a default value if HasValue is false. More...
void	Then (Action< T > then)
R	Then< R > (Func< T, R > then, Func< R > @else)
R	Then< R > (Func< T, R > then, R defaultValue)

Static Public Member Functions
static implicit	operator Maybe< T > (T value)
static implicit	operator Maybe< T > (NoValue _)

Member Function Documentation

T Loyc.Maybe< T >.Or ( T  defaultValue )

inline

Converts Maybe{T} to T, returning a default value if HasValue is false.

This is equivalent to the ?? operator of T?.