Parentheses delimit method arguments in Ruby. They are often optional, but adding them can remove ambiguity and make a method call easier to read. section 1.1.4
Making the argument boundary explicit
Both "100".to_i and "100".to_i(9) call to_i, but the second form visibly supplies 9 as an argument and converts the string as a base-9 number, producing 81. section 1.1.4
Parentheses also help Ruby distinguish method calls from nearby syntax:
- An identifier followed by parentheses is parsed as a method call, including an empty call such as x(). Without parentheses, an unresolved identifier may be reported as either an undefined local variable or method. section 2.5.4
- A hash used as the first argument must be enclosed in curly braces and placed inside parentheses; otherwise Ruby can interpret the braces as a code block. section 9.3.7
- A final hash argument may omit its curly braces, but parentheses around the complete argument list clarify where the arguments begin and end. section 9.3.7
x = "100".to_i
Compare a method call without an explicit argument list to the same call with parentheses and an argument. section 1.1.4
my_method({ NY: "New York" }, 100, "another argument")
Use parentheses to force a leading hash to remain a method argument rather than a code block. section 9.3.7
