Question

I’m getting to grips with rails and whilst I feel I am progressing there is one thing that I am struggling to get to grips with and it’s very basic. I am trying to understand the different usage of [] {} and () Are there any good sources of their usage and are there any tips you can give to a beginner in recognizing when to use one or the other, or as I seem to see in some cases when they are not required at all?
I know this is extremely basic but I have struggled to find literature which explains concisely the interplay between them and Ruby or specifically RoR

Answer 1

It has nothing to do with RoR; the various brackets are Ruby language constructs.

[] is the array operator, for arrays and other classes that implement it (like a string taking a range to get substrings, or hashes to look up a key’s value):

a = [1, 2, 3]
a.each { |n| puts n }

s = "ohai"
puts s[1..-1]

h = { foo: "bar", baz: "plugh" }
puts h[:foo]

{} is for hashes, and one of two ways of delimiting blocks (the other being begin/end). (And used with # for string interpolation.)

h = { foo: "bar", baz: "plugh" }
h.each { |k, v| puts "#{k} == #{v}" }

() is for method parameters, or for enforcing evaluation order in an expression.

 > puts 5 * 3 + 5     # Normal precedence has * ahead of +
=> 20
 > puts 5 * (3 + 5)   # Force 3+5 to be evaluated first
=> 40

def foo(s)
  puts(s)
end

They’re sometimes optional if the statement has no ambiguity:

def foo s
  puts s
end

(They’re not always optional, and putting a space between the method call and its parenthetical parameter list can cause issues–best not to, IMO.)

(I probably missed something, too, but there’s the nutshell.)