73 lines
6.9 KiB
Markdown
73 lines
6.9 KiB
Markdown
# Inspired by F#
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This project contains PHP utility classes whose functionality is inspired by their F# counterparts.
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The v2 series requires at least PHP 8.4. A similar API exists for PHP 8.2 - 8.3 in version 1 of this project; see its README for specifics.
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## What It Provides
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This early-stage library currently provides two classes, both of which are designed to wrap values and indicate the state of the action that produced them. `Option<T>` represents a variable that may or may not have a value. `Result<TOK, TError>` represents the result of an action; the "ok" and "error" states both provide a value.
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| | `Option<T>`<br>Replaces `null` checks | `Result<TOK, TError>`<br>Replaces exception-based error handling |
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|---------------------------------------------------|-------------------------------------------------------|-----------------------------------------------------------------------------|
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| **Creating** | `::Some(T)` for Some | `::OK(TOK)` for OK |
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| | `::None()` for None | `::Error(TError)` for Error |
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| | `::of($value)` _None if `null`_ | |
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| **Querying** | `->isSome: bool` | `->isOK: bool` |
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| | `->isNone: bool` | `->isError: bool` |
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| | `->contains(T, $strict = true): bool` | `->contains(TOK, $strict = true): bool` |
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| | `->exists(callable(T): bool): bool` | `->exists(callable(TOK): bool): bool` |
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| **Reading**<br> | `->value: T` | `->ok: TOK` |
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| _all throw if called on missing value_ | | `->error: TError` |
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| **Transforming**<br> | `->map(callable(T): TMapped): Option<TMapped>` | `->map(callable(TOK): TMapped): Result<TMapped, TError>` |
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| _all still `Option` or `Result`_ | | `->mapError(callable(TError): TMapped): Result<TOK, TMapped>` |
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| **Iterating** | `->iter(callable(T): void): void` | `->iter(callable(TOK): void): void` |
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| **Inspecting**<br>_returns the original instance_ | `->tap(callable(Option<T>): void): Option<T>` | `->tap(callable(Result<TOK, TError>): void): Result<TOK, TError>` |
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| **Continued Processing** | `->bind(callable(T): Option<TBound>): Option<TBound>` | `->bind(callable(TOK): Result<TBoundOK, TError>): Result<TBoundOK, TError>` |
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| **Changing Types** | `->toArray(): T[]` | `->toArray(): TOK[]` |
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| | | `->toOption(): Option<TOK>` |
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In addition to this, `Option<T>` provides:
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- `->getOrDefault(T)` will return the Some value if it exists or the given default if the option is None.
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- `->getOrCall(callable(): mixed)` will call the given function if the option is None. That function may return a value, or may be `void` or `never`.
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- `->getOrThrow(callable(): Exception)` will return the Some value if it exists, or throw the exception returned by the function if the option is None.
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- `->filter(callable(T): bool)` will compare a Some value against the callable, and if it returns `true`, will remain Some; if it returns `false`, the value will become None.
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- `->unwrap()` will return `null` for None options and the value for Some options.
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Finally, we would be remiss to not acknowledge some really cool prior art in this area - the [PhpOption](https://github.com/schmittjoh/php-option) project. `Option::of` recognizes their options and converts them properly, and `Option<T>` instances have a `->toPhpOption()` method that will convert these back into PhpOption's `Some<T>` and `None` instances. There is also a [ResultType](https://github.com/GrahamCampbell/Result-Type) project from the same team, though this project's result does not (yet) have any conversion methods for it.
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## The Inspiration
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[F#](https://fsharp.org/) is an ML-style language that runs under .NET. It has most of the functional programming paradigms, but as it runs on what was designed as an object-oriented runtime - and can use and interoperate with all the .NET libraries - it is a pragmatic approach to functional programming. (Many of its decade+ old features have been implemented into recent versions of C#.)
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This library, too, makes some pragmatic choices about structure. In F#, for example, an optional value could be obtained like...
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```fsharp
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let value =
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Option.ofObj myVar
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|> Option.map (fun it -> it.Replace("howd", "part"))
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|> Option.defaultValue "There was no string"
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```
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If `myVar` were `null`, this `value` would have "There was no string"; if `myVar` had "howdy", `value` would have "party". Each `Option` call takes the option as its last parameter, and `|>` is the pipeline operator; it provides the previous value as the last parameter to the next operation. A prior version of this library had static functions to mimic this, which resulted in something like...
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```php
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$value = Option::defaultValue('There was no string',
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Option::map(fn($it) => str_replace('howd', 'part', $it),
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Option::of($myVar)));
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```
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...which reads right-to-left (or bottom-to-top, the way it is formatted there). By implementing these as instance methods, the PHP code looks much cleaner.
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```php
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$value = Option::of($myVar)
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->map(fn($it) => str_replace('howd', 'part', $it))
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->getOrDefault('There was no string');
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```
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If PHP gets a pipeline operator, we'll revisit lots of stuff here (in a non-breaking way, of course).
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## Ideas
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This library currently has the features which its author needs. To suggest others, reach out to Daniel on the Fediverse at @daniel@fedi.summershome.org or on Twitter at @Bit_Badger.
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