Nullable type

Q: How deeply does F# in Action: A Revised Edition of Get Programming with F# cover nullable type?

Explains the modeling problem, historical solution, boundary conversions, and preferred F# usage without detailing Nullable internals.

As explained in F# in Action: A Revised Edition of Get Programming with F#

Nullable<T> is a .NET value type that represents either a value of a non-nullable value type or the absence of such a value.

A nullable type represents either a value-type value or the absence of a value. It lets application models represent unset numbers without reserving magic values such as -1, including values that originate in SQL databases. section 9.1.1

In F#, use Option throughout domain code rather than mixing Nullable<T>, naked nulls, and options. Convert at .NET boundaries, then convert back when returning data to .NET consumers. section 9.1.5

Convert nullable values at an F# boundary

Use Option.ofNullable to turn a .NET nullable into an F# option, and Option.toNullable when data must cross back into .NET code. This keeps missing-value handling uniform inside the F# domain. section 9.1.5

open System
 
let optionalName : string option = null |> Option.ofObj   #1
let optionalNameTwo = "Isaac" |> Option.ofObj             #2
let optionalAge = Nullable() |> Option.ofNullable         #3
let optionalAgeTwo = Nullable 123 |> Option.ofNullable    #4

Compare empty and populated Nullable values after converting them into options with Option.ofNullable; the same boundary pattern applies to .NET objects through Option.ofObj. section 9.1.5

How F# in Action: A Revised Edition of Get Programming with F# covers it

Cover of F# in Action: A Revised Edition of Get Programming with F#

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Also explained in

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Kotlin in Action, 2EA nullable type is a type whose values may include null and whose unsafe operations are restricted by the type system.
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Pro ASP.NET Core 7, Tenth EditionA nullable parameter type is a parameter type that permits a null value to represent the absence of a supplied argument.

Compare how 3 books explain nullable type →

Related concepts

Kotlinused by · Kotlin is a statically typed general-purpose programming language that targets the JVM and other platforms and interoperates with Java.
non-nullable typecontrasts with · A non-nullable type is a type whose values are statically constrained not to include the null value.
missing valueuses · A missing value is a marker or condition indicating that an expected data value or reference is absent, unavailable, unknown, or inapplicable.
..< operatoruses · The `..<` operator constructs a range that includes its lower endpoint and excludes its upper endpoint.
operatoruses · An operator is a symbol, keyword, or language construct that specifies an operation on one or more operands.

This explainer was generated by Manning's knowledge graph from the text of F# in Action: A Revised Edition of Get Programming with F#. The section links point to the parts of the book it draws on.