ruby-rbs

Ruby RBS Type Signatures

RBS is Ruby's official type signature language for describing the structure of Ruby programs - classes, modules, methods, and types. This skill covers both approaches to adding types:

1. Inline RBS (# rbs_inline: enabled) - Type annotations embedded in Ruby source files as comments
2. Standalone RBS files (.rbs) - Separate signature files that describe Ruby code

Choosing an Approach

Aspect	Inline RBS	Standalone .rbs Files
Co-location	Types live with code	Types in separate sig/ directory
Ruby files	Modified with comments	Unchanged
Tooling	Requires rbs-inline gem	Native RBS support
Use case	New code, gradual adoption	Libraries, gems, existing codebases

Use inline RBS when: Starting fresh, want types near code, prefer gradual typing Use standalone .rbs when: Publishing gems, typing third-party code, complete API documentation

Subskills

For detailed guidance on each approach:

• subskills/inline/SKILL.md - Writing inline RBS annotations in Ruby files
• subskills/rbs-files/SKILL.md - Writing standalone .rbs signature files

Core Type Syntax (Both Approaches)

Basic Types

String              # String instance
Integer             # Integer instance
Float               # Float instance
bool                # true | false
boolish             # Any truthy/falsy value (for predicates)
nil                 # nil value
void                # Return value not used
untyped             # Skip type checking (gradual typing)
top                 # Supertype of all types
bot                 # Subtype of all types (never returns)
self                # Type of receiver
instance            # Instance of the class
class               # Singleton class

Compound Types

String?                              # Optional: String | nil
String | Integer                     # Union type
_Reader & _Writer                    # Intersection type
Array[String]                        # Generic class
Hash[Symbol, Integer]                # Hash with typed keys/values
[String, Integer]                    # Tuple (fixed-size array)
{ name: String, age: Integer }       # Record (typed hash)
{ name: String, age?: Integer }      # Record with optional key
^(Integer) -> String                 # Proc/lambda type