swift-casification

Package for tokenizing and applying case transformations to arbitrary strings.

Table of contents

• Motivation
• Usage
  • Basic modifiers
  • Token-based modifiers
  • Composing modifiers
  • Custom modifiers
• Installation
• License

Motivation

Swift does not provide a standard way to tokenize strings or to build formatted strings from such tokens.

As a result, even common transformations like camelCase are often implemented differently across projects, leading to duplicated logic and inconsistent results.

This package focuses on providing a set of predefined, reusable string modifiers for common casing and formatting transformations, with consistent behavior across codebases.

Usage

A set of predefined string modifiers is available out of the box

Basic modifiers

Modifiers	Examples
upper	some string → SOME STRING
lower	Some string → some string
upperFirst	some String → Some String
lowerFirst	Some string → some String
capital	some string → Some String
swap	Some String → sOME sTRING

Token-based modifiers

Those modifiers are a bit more complex and do support configuration

Modifiers	Examples
camel(.camel)	camel
camel(.pascal)	pascal
camel	camel(.camel)
pascal	camel(.pascal)
camel(.automatic)	camel()
camel(.automatic)	camel()
snake	some string 1 x value → some_string_1x_value
kebab	some string 1 x value → some-string-1x-value
dot	some string 1 x value → some.string.1x.value

Note

See Tests for more examples

Configuration

Tokenization uses list of acronyms to properly handle common values like UUID, but the list is limited and statically defined, which may lead to tokenization misses for such values. Tokenization misses will lead to incorrect formatting for some modifiers.

There are 2 ways to override existing acronyms

First one is overriding default values globally using prepareConfiguration(_:) function and should be performed at the application start (as early as possible):

String.Casification.prepareConfiguration { 
  $0.acronyms.formUnion(["uml", "Uml", "UML"])              
}

"uml_string".case(.pascal) // UMLString

Second one is providing contextual override using withAcronyms(_:operation:) function:

"uml_string".case(.pascal) // UmlString

withAcronyms { $0 
  .formUnion(["uml", "Uml", "UML"]) 
} operation: {
  "uml_string".case(.pascal) // UMLString
}

Tip

Explore Configuration to find out more about available options, for example predefined modifiers do handle numbers gently out-of-the box:

"1.23 in a Sentence".case(.pascal) → "1_23_InASentence"

"Lens1x".case(.snake) → "lens_1x" instead of "lens_1_x"

"Grid1x1".case(.camel) → "grid_1x1" instead of "grid_1_X_1"

Though you can disable this behavior with:

String.Casification.prepareConfiguration {
  // Default is `[.singleLetter([.disableSeparators, .disableNextTokenProcessing])]`
  $0.common.numbers.boundaryOptions = []
  
  // You can also enable allowed delimeters
  // "1.23 String".case(.snake) -> 1.23_string
  $0.common.numbers.allowedDelimeters = ["."]
}

Camel

Camel case modifiers do also support advanced configuration

You can use explicit parameters:

"string_id".case(.camel()) // stringID

withCasification { $0.camelCase.acronyms.processingPolicy = .alwaysCapitalize } operation: {
	"string_id".case(.camel(.)) // stringId
}

You can override default config using prepareConfiguration(_:) function and it also should be performed at the application start (as early as possible):

String.Casification.prepareConfiguration {
  $0.camelCase.acronyms.processingPolicy = .alwaysCapitalize
}

"string_id".case(.camel()) // stringId

Composing modifiers

Modifiers can be combined using combined(with:) method. Order matters – transformations are applied sequentially.

// "myString" → "mystring" → "Mystring"
"myString".case(.lower.combined(with: .upperFirst))

// "myString" → "Mystring" → "mystring"
"myString".case(.upperFirst.combined(with: .lower)) // mystring

Custom modifiers

For simple modifiers, conforming a type to String.Casification.Modifier is enough

extension String.Casification.Modifiers {
  /// Deletes input string
  public struct Delete: String.Casification.Modifier {
    public init() {}
    
    @inlinable 
    public func transform(_ input: Substring) -> Substring {
      ""
    }
  }
}

Tip

It's a good idea to declare convenience accessor for the protocol

extension String.Casification.Modifier
where Self == String.Casification.Modifiers.Delete {
     public var delete: Self { .init() }
}

"myString".case(.delete) // ""

For more complex processing, you can operate on tokens instead of raw strings by conforming to String.Casification.TokensProcessor

extension String.Casification.TokensProcessors {
  public struct RemoveSeparators: String.Casification.TokensProcessor {
    public init() {}
    @inlinable
    public func processTokens(
      _ tokens: ArraySlice<String.Casification.Token>
    ) -> ArraySlice<String.Casification.Token> {
      return tokens.filter { $0.kind != .separator }[...]
    }
  }
}

extension String.Casification.TokensProcessor
where Self == String.Casification.TokensProcessors.RemoveSeparators {
  public static var removeSeparators: Self { .init() }
}

extension String.Casification.Modifier
where Self == String.Casification.Modifiers.AnyModifier {
  public var noSeparators: Self {
    .processingTokens(with: .removeSeparators)
  }
}

"my test-string".case(.noSeparators) // "myteststring"

Note

The package is primarily designed around predefined reusable modifiers. Custom modifiers are supported, but declarations can be verbose due to namespacing and generic types.

Installation

Basic

You can add swift-casification to an Xcode project by adding it as a package dependency.

1. From the File menu, select Swift Packages › Add Package Dependency…
2. Enter "https://github.com/capturecontext/swift-casification" into the package repository URL text field
3. Choose products you need to link to your project.

Recommended

If you use SwiftPM for your project structure, add swift-casification dependency to your package file

.package(
  url: "https://github.com/capturecontext/swift-casification.git", 
  .upToNextMinor("0.5.0")
)

Do not forget about target dependencies

.product(
  name: "Casification", 
  package: "swift-casification"
)

License

This library is released under the MIT license. See LICENSE for details.