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https://github.com/propensive/galilei

Simple interfaces for I/O operations in Scala
https://github.com/propensive/galilei

disk files filesystem filesystem-library io paths scala

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Simple interfaces for I/O operations in Scala

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# Galilei



__Making I/O in Scala elegant and typesafe__



__Galilei__ is a library for performing safe disk I/O with Scala. It uses dependent types to provide

precise static representations of paths, files, directories and other filesystem objects, enforcing

filesystem-aware constraints on filenames and metadata. Galilei has a particular focus on precise error

handling and, when enabled, each filesystem operation which might fail must be handled for each possible

failure type; but its innovation is in minimizing that to a set of failure types which depends not

just on the operation, but also the filesystem and in-scope options.



## Features



- intuitive and instructive API for most common filesystem operations

- safe and precise error handling, without unnecessary handling

- read from and write to files on disk with a variety of different types



## Availability



## Getting Started



### Example



For example, moving a file from `/home/work/file` to `/home/work/copy` should work fine

if there is no pre-existing file at `/home/work/copy`. We can move it with,

`file.moveTo(destination)`. But if `/home/work/copy` already

exists, then we may or may not care about what happens if we try to overwrite it.



The behavior can be specified with a contextual value in scope. Either,

```scala

import filesystemOptions.overwritePreexisting

```

or,

```scala

import filesystemOptions.doNotOverwritePreexisting

```



The `moveTo` operation does not assume one option or the other as a default, and Galilei's

philosophy is that it would be wrong to do so. Instead, invoking `moveTo` _without_ exactly

one of the two contextal values in scope is a compile error, and the user is forced to

decide on the correct behavior. This is both unpresumptuous and instructive, since the

user may not have even considered the decision had to be made.



As a contextual value, the choice of behavior can be limited to a narrow scope, or

imported globally, as needed.



If Scala 3's "safer exceptions" are turned on, then the choice of behavior also affects

which exceptions must be handled when calling `moveTo`. The method invocation may throw

an `IoError` under any circumstances, so that must always be handled, but with

`doNotOverwritePreexisting` in scope, if there _is_ a pre-existing file at the destination,

then an `OverwriteError` will be thrown, which must be handled.



But since it cannot be thrown with `overwritePreexisting` in scope, the obligation to handle it

is also removed.



### Types



Unlike many disk I/O libraries, __Galilei__ provides different types for `Path`s, `File`s, `Directory`s

and other types of node, like `Symlink`s. A `Path` represents the abstract notion of a location within

a filesystem, which may or may not exist and may be a file, a directory or (on Linux, at least) one of

several other filesystem node types. Types such as `File` and `Directory` should only exist to

correspond to a real file or directory on disk.



Of course, the contents of a filesystem can change independently of the JVM, so the existence of

an immutable `File` or `Directory` instance does not guarantee its eternal existence on disk, but

we do, at least, guarantee that the filesystem node existed and had the correct type at the time

of the object's creation.



## Status



Galilei 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.



Galilei is designed to be _small_. Its entire source code currently consists

of 965 lines of code.



## Building



Galilei 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 Galilei?".



1. *Copy the sources into your own project*

   

   Read the `fury` file in the repository root to understand Galilei'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](https://github.com/propensive/wrath/)*



   Wrath is a bootstrapping script for building Galilei 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`](https://github.com/propensive/wrath/releases/latest), 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 `galilei`.

   Run `wrath -F` in the repository root. This will download and compile the

   latest version of Scala, as well as all of Galilei's dependencies.



   If the build was successful, the compiled JAR files can be found in the

   `.wrath/dist` directory.



## Contributing



Contributors to Galilei are welcome and encouraged. New contributors may like

to look for issues marked

[beginner](https://github.com/propensive/galilei/labels/beginner).



We suggest that all contributors read the [Contributing

Guide](/contributing.md) to make the process of contributing to Galilei

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



Galilei was designed and developed by Jon Pretty, and commercial support and

training on all aspects of Scala 3 is available from [Propensive

OÜ](https://propensive.com/).



## Name



Galilei's primary focus is handling Input and Output, or _I/O_, and is a pun on the name of the moon _Io_, one of the four moons of Jupiter discovered by Galileo Galilei.



### Pronunciation



`/ˌɡælɪˈleɪ/`



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 is the Galilean planet, Io.



## License



Galilei is copyright © 2024 Jon Pretty & Propensive OÜ, and

is made available under the [Apache 2.0 License](/license.md).