A simple representation of optional values

Scala's Option is the traditional way to represent values which may be either present (in which case a value is specified) or absent. Option is a simple ADT, but union types, along with some helper methods, can provide much better ergonomics in most circumstances. Vacuous offers an Optional type which provides this functionality.

• Provides an implementation of optional values using union types
• No need to wrap present values in Some
• Flattened representation, prohibiting ambiguous Some(None) representation
• Lightweight let, lay and or methods cover map, flatMap, fold, orElse and getOrElse
• Performant inlined implementations of all critical methods
• Especially convenient use case for default parameters

Vacuous has not yet been published. The medium-term plan is to build it with Fury and to publish it as a source build on Vent. This will enable ordinary users to write and build software which depends on Vacuous.

Subsequently, Vacuous will also be made available as a binary in the Maven Central repository. This will enable users of other build tools to use it.

For the overeager, curious and impatient, see building.

An optional value, which might be an instance of ValueType, or may be absent, may be given the type Optional[ValueType]. If it is absent, then it has the value, Unset, which is a singleton object. Optional[ValueType] is an alias for the union type, ValueType | Unset.type.

Note that the declarations,

val value: Text = t"Hello world"

and,

val value: Optional[Text] = t"Hello world"

differ only in their types; the syntax of the expression is identical, and does not need to be wrapped with another factory method, like Some.

Since union types are unordered sets of types, nesting two Optionals, for example in Optional[Optional[Int]] expands to Int | Unset.type | Unset.type, which is identical to Int | Unset.type. And this is the same as Optional[Int]. While there is nothing to prevent nesting one Optional within another Optional, it's impossible to distinguish between the types, and impossible for an Unset value to be considered present rather than absent; it is the definition of absence.

An Optional[Text] value may seem very similar to a Text value, but the possibility that it might be Unset makes it impossible to use any methods defined on Text on an Optional[Text], since those methods are not applicable to just one of the possible values of the type, Unset. So several convenience methods are provided to make Optionals easy to work with.

The method or replaces the Unset value with another value, eliminating the optionality from the type. This is equivalent to both getOrElse and orElse on Option. This equivalence comes from the lack of nesting of Optional values.

Similarly, let applies a lambda to the present values, and leaves the absent value unchanged. It is equivalent to both map and flatMap on Options.

Finally, lay combines or and let in a single, two-parameter method: the alternative value for Unset is specified first, followed by the lambda mapping the present values. This is equivalent to fold on an Option.

These method names were deliberately chosen to be short, as they are intended to be used frequently and are rarely the most interesting part of an expression.

Vacuous is classified as maturescent. For reference, Soundness projects are categorized into one of the following five stability levels:

• embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
• fledgling: of proven utility, seeking contributions, but liable to significant redesigns
• maturescent: major design decisions broady settled, seeking probatory adoption and refinement
• dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version 1.0.0 or later
• adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated

Projects at any stability level, even embryonic projects, can still be used, as long as caution is taken to avoid a mismatch between the project's stability level and the required stability and maintainability of your own project.

Vacuous is designed to be small. Its entire source code currently consists of 110 lines of code.

Vacuous will ultimately be built by Fury, when it is published. In the meantime, two possibilities are offered, however they are acknowledged to be fragile, inadequately tested, and unsuitable for anything more than experimentation. They are provided only for the necessity of providing some answer to the question, "how can I try Vacuous?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Vacuous's build structure, dependencies and source location; the file format should be short and quite intuitive. Copy the sources into a source directory in your own project, then repeat (recursively) for each of the dependencies.

   The sources are compiled against the latest nightly release of Scala 3. There should be no problem to compile the project together with all of its dependencies in a single compilation.

2. Build with Wrath

   Wrath is a bootstrapping script for building Vacuous and other projects in the absence of a fully-featured build tool. It is designed to read the fury file in the project directory, and produce a collection of JAR files which can be added to a classpath, by compiling the project and all of its dependencies, including the Scala compiler itself.

   Download the latest version of wrath, make it executable, and add it to your path, for example by copying it to /usr/local/bin/.

   Clone this repository inside an empty directory, so that the build can safely make clones of repositories it depends on as peers of vacuous. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Vacuous's dependencies.

   If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributors to Vacuous are welcome and encouraged. New contributors may like to look for issues marked beginner.

We suggest that all contributors read the Contributing Guide to make the process of contributing to Vacuous easier.

Please do not contact project maintainers privately with questions unless there is a good reason to keep them private. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.

Vacuous was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

Something which is vacuous is empty; devoid of content. Vacuous provides representation for values which may be thus.

In general, Soundness project names are always chosen with some rationale, however it is usually frivolous. Each name is chosen for more for its uniqueness and intrigue than its concision or catchiness, and there is no bias towards names with positive or "nice" meanings—since many of the libraries perform some quite unpleasant tasks.

Names should be English words, though many are obscure or archaic, and it should be noted how willingly English adopts foreign words. Names are generally of Greek or Latin origin, and have often arrived in English via a romance language.

The logo shows a stylized pressure gauge, reading zero.

Vacuous is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.