TopolearnText processing is everywhere, and Ruby's string API plus symbols are used in every Ruby program.
Double-quoted strings interpolate with #{} and process escapes: "Hi #{name}\n". Single-quoted strings are literal. Heredocs build multi-line text, and the squiggly form <<~TEXT strips the common leading indentation.
The String API is large and readable: upcase, capitalize, strip, split, include?, start_with?, sub/gsub (with strings or regexes), center, ljust, * for repetition, and [] with an index, range or regex. format("%.2f", x) and "%05d" % n format numbers.
Ruby strings are mutable. << appends in place, and bang methods like upcase! modify the receiver (returning nil if nothing changed). Non-bang methods return a new string. Two variables can share one string object, so in-place changes are visible through both.
Adding # frozen_string_literal: true at the top of a file makes all literals frozen (immutable). In Ruby 3.4, literals in files without the comment are "chilled": mutating them still works but emits a deprecation warning when deprecation warnings are enabled, as a step toward frozen literals by default. Use +"" or String.new when you need a mutable buffer.
A Symbol like :status is an immutable name; the same symbol is always the same object. Use symbols for identifiers and hash keys, strings for text data. str.to_sym and sym.to_s convert between them.
Example
# frozen_string_literal: true
name = "Ruby"
puts "Hi #{name}, #{name.length} chars" # Hi Ruby, 4 chars
puts 'No #{interp} here' # No #{interp} here
text = <<~MSG
Dear #{name},
indented line
MSG
puts text # leading indentation removed
puts "a,b,,c".split(",").inspect # ["a", "b", "", "c"]
puts "hello world".gsub(/o/, "0") # hell0 w0rld
puts format("%.2f|%5s|", 3.14159, "x") # 3.14| x|
buf = +"" # mutable even with frozen literals
buf << "a" << "b"
puts buf # ab
puts "lit".frozen? # true (magic comment)
puts :ok.equal?(:ok) # true: one object per symbolRemember
- Use "#{}" for interpolation and <<~ for indented heredocs
- Bang methods and << mutate; most other methods return new strings
- Symbols are immutable identifiers; strings are text data
Watch out for
- Modifying a string that another variable also references, then being surprised both changed.