Gossamer

Lightweight string utilities

The Java implementation of String provides many methods which are useful, but some lack sufficient typesafety. Gossamer provides the Text type, a more typesafe opaque type alias of String.

Features

• reimplements common methods on String with more typesafe variants
• provides an implementation of the Minimum Edit Distance algorithm
• convenient converters to common encodings like URL encodings and Punycode
• implements a stricter t"" interpolator for strings
• implements the txt"" interpolator to ignore spurious whitespace in strings which flow onto multiple lines

Availability

Getting Started

Gossamer provides a collection of useful methods and constructors for working with strings.

All Gossamer terms and types are defined in the gossamer package:

import gossamer.*

Show typeclass

A standard Show typeclass is provided which will convert values of different types into Strings.

Many types, such as Ints, only have a single reasonable presentation as a String, while others, for example instances of case classes, may be presented in different ways depending on the context. Gossamer's Show typeclass does not prescribe exactly where and when it should be used, but instances of Show should produce strings which meaningfully present a value as a string, usually for human consumption.

Using Wisteria, Show instances for product types (such as case classes and tuples) and coproduct types (such as enumerations and sealed traits) will be automatically derived.

Text, a typesafe String

The Text type in anticipation is provided as an opaque alias of String, duplicating most of the functionality of String (and its associated extension methods), but without the typesafety risks associated with String. Text instances may only be combined with other types when a Show typeclass instance exists for that type.

Furthermore, every method of Text is guaranteed not to be null and declares any exceptions it may throw.

Interpolators

Scala's standard library provides the s interpolator which allows elements of any type to be substituted into a String. This presents a typesafety hole, since toString must be applied to each one, without any guarantee that it produces a reasonable presentation of that value as a String.

So Gossamer introduces the str"" interpolator which only permits types with a corresponding Show typeclass instance to be substituted into a string: other types will result in an error. The toString method will never be called on these substitutions.

Long strings

Additionally, a txt"" interpolator is provided for constructing "long" strings which need to be split across several lines of code, but where any whitespace (such as indentation and newlines) should always be read as a single space character, unless it contains two adjacent newlines, in which case it should be interpreted as a "new paragraph", represented as a single newline ('\n') character.

This is particularly useful for embedding long messages in code while not breaking the consistency of indentation. For example:

import anticipation.Text

val msg: Text = txt"""This is a long message which will not fit into a
                      standard line of code, and needs to be split across
                      several lines.

                      But at least it is aligned nicely within the code."""

The String msg will contain a single '\n' character, between lines. and But.

DebugString typeclass

In addition to Show, Gossamer provides a DebugString single-abstract-method typeclass which is designed to provide String representations of values as valid Scala expressions that could be copied and pasted into code.

Like the Show typeclass, product and coproduct instances of DebugString are automatically derived.

Encodings

Simple extension methods which provide a number of string-based encodings are provided. The urlEncode and urlDecode methods will convert to and from (respectively) strings in the URL encoding scheme. The punycode method will convert the string (most commonly, a domain name) into a ASCII-only representation of the string, encoding any non-ASCII characters as Punycode.

Safer String methods

Safer alternatives to many of the commonly-used methods of String are provided. These typically delegate to existing methods on String, but will:

• never return null
• never return mutable arrays
• never accept Any as a parameter type, or implicitly use String#toString to convert non-String types to Strings

Minimum Edit Distance

An implementation of the Minimum Edit Distance or Levenshtein distance, lev is provided as an extension method on Texts. The method takes another Text as a parameter, and returns the minimum number of edits (character additions, deletions or replacements) required to change one string to the other.

For example, t"Hello".lev(t"Hallo!") returns 2: the replacement of e with a counts as one edit, and the addition of ! counts as the second edit. The algorithm is symmetrical.

Joining

Scala's standard library provides the mkString method on collection types, but this unfortunately calls toString on every element in the collection, without warning. Gossamer provides a join method which may only be applied to values that are already Strings.

This is further generalized with a Joinable typeclass: if an instance exists for other String-like types, they may also be joined like a collection of Strings, where every parameter to join is of the same type as the elements of the collection.

In addition to the zero-, one- and three-parameter variants of join which behave like their mkString equivalents, two- and four-parameter versions are also provided. These allow a different separator to be used between the penultimate and last elements of the collection.

For example,

val numbers = List(t"one", t"two", t"three", t"four").join(t", ", t" and ")

will evaluate to "one, two, three and four", and,

val numbers2 = List(t"one", t"two", t"three").join(t"Choose ", t", ", t" or ", t".")

results in, t"Choose one, two or three.".

Status

Gossamer is classified as fledgling. 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.

Gossamer is designed to be small. Its entire source code currently consists of 1211 lines of code.

Building

Gossamer 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 Gossamer?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Gossamer'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 Gossamer 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 gossamer. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Gossamer's dependencies.

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

Contributing

Contributors to Gossamer 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 Gossamer 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.

Author

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

Name

Gossamer is lightweight and stringlike.

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.

Logo

The logo shows the glowing tip of a gossamer-thin fibreoptic cable.

License

Gossamer is copyright © 2025 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.