TopolearnRuby's simple truthiness rule and its numeric types shape how every condition and calculation behaves.
Local variables need no declaration: count = 3. Names are snake_case. Constants start with a capital letter, MAX_SIZE = 10, and Ruby warns if you reassign one.
Core value types:
- Integer has arbitrary precision:
2**100just works. Integer division truncates toward negative infinity:7 / 2is3and-7 / 2is-4. Use7.fdiv(2)or a float operand for3.5. - Float is a double:
0.1 + 0.2is0.30000000000000004. UseRationalorBigDecimalfor money. - String is mutable text, and Symbol (
:name) is an immutable, interned name, mostly used as hash keys and identifiers. true,falseandnil("no value").
The truthiness rule is simple: only `false` and `nil` are falsy. 0, "" and [] are all truthy, unlike in many languages. Check for nothing with x.nil? and for emptiness with empty?.
Conversions are explicit: "42".to_i, "3.5".to_f, 42.to_s, :sym.to_s, "str".to_sym. The lenient "12abc".to_i returns 12; the strict Integer("12abc") raises ArgumentError, which is what you want for validating input.
x ||= 5 assigns only if x is nil or false, a common idiom for defaults and memoisation. Safe navigation user&.name returns nil instead of raising when user is nil.
Example
count = 3
price = 9.5
big = 2**100
puts big # 1267650600228229401496703205376
puts 7 / 2, -7 / 2 # 3, -4
puts 7.fdiv(2) # 3.5
puts 0.1 + 0.2 # 0.30000000000000004
puts "zero is truthy" if 0 # zero is truthy
puts [nil, false, 0, ""].map { |v| v ? "T" : "F" }.join # FFTT
puts "12abc".to_i # 12
begin
Integer("12abc")
rescue ArgumentError
puts "strict parse failed" # strict parse failed
end
name = nil
name ||= "guest"
p name # "guest"
p nil&.length # nilRemember
- Only false and nil are falsy; 0 and "" are truthy
- Integers are arbitrary precision and / on integers truncates
- Use Integer() and Float() for strict parsing, to_i for lenient
Watch out for
- Writing if count.zero? style checks as if count, which is always true for numbers.