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Literal constructor

As explained in The Well-Grounded Rubyist, Fourth Edition

A literal constructor is syntax that creates a value or object directly without an explicit call to a class constructor method such as new.

A literal constructor creates certain Ruby objects through dedicated syntax instead of an explicit call to new. Using one brings a new object into existence, and these forms are common even when another instantiation route exists. section 7.1

Ruby’s built-in literal constructors include:

  • Strings: "new string" or 'new string'. section 7.1
  • Symbols: :symbol or :"symbol with spaces"; Symbol has no new constructor. section 7.1
  • Arrays: [1, 2, 3, 4, 5]; hashes: {"New York": "NY", "Oregon": "OR"}. section 7.1
  • Ranges: 0..9 or 0...10; regular expressions: /([a-z]+)/. section 7.1
  • Procs and lambdas: ->(x, y) { x * y }. section 7.1

Notation versus new

String.new and Array.new explicitly invoke new, while "new string" and [1, 2, 3] create objects through literal syntax. The notation is not interchangeable with every use of similar punctuation: [] can be a literal array constructor or a call to an object's [] method, and curly braces can delimit a code block rather than a hash literal. Context determines the meaning. section 7.1

Table 7.1 Built-in Ruby classes with literal constructors

Class

Literal constructor

Example(s)

String

Quotation marks

"new string"

'new string'

Symbol

Leading colon

:symbol

:"symbol with spaces"

Array

Square brackets

[1,2,3,4,5]

Hash

Curly braces

{"New York": "NY", "Oregon": "OR"}

Range

Two or three dots

0..9 or 0...10

Regexp

Forward slashes

/([a-z]+)/

Proc (lambda)

Dash, arrow, parentheses, braces

->(x,y) { x * y }

Compare Ruby classes with their literal constructor characters and concrete examples. section 7.1

How The Well-Grounded Rubyist, Fourth Edition covers it

How deep it goes
Defines the feature, catalogs its forms, and explains notation ambiguity without detailing object-creation internals.
Examples
Uses strings, symbols, arrays, hashes, ranges, regular expressions, lambdas, String.new, Array.new, and ambiguous [] or {} notation.
What it assumes
Assumes familiarity with Ruby classes, objects, methods, and basic syntax while reinforcing built-in object creation.
What you can do after
Evaluate Ruby punctuation correctly and recognize when it creates a literal object or invokes a method in context.
How it connects
Connects literal constructors with classes, objects, new, conversion methods, syntactic sugar, operator overloading, and code blocks.
Cover of The Well-Grounded Rubyist, Fourth Edition
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of The Well-Grounded Rubyist, Fourth Edition. The section links point to the parts of the book it draws on.