What do the different brackets in Ruby mean?

Question

In Ruby, what\'s the difference between {} and []?

{} seems to be used for both code blocks and hashes.

Are []

Answer 1

The square brackets [ ] are used to initialize arrays. The documentation for initializer case of [ ] is in

ri Array::[]

The curly brackets { } are used to initialize hashes. The documentation for initializer case of { } is in

ri Hash::[]

The square brackets are also commonly used as a method in many core ruby classes, like Array, Hash, String, and others.

You can access a list of all classes that have method "[ ]" defined with

ri []

most methods also have a "[ ]=" method that allows to assign things, for example:

s = "hello world"
s[2]     # => 108 is ascii for e
s[2]=109 # 109 is ascii for m
s        # => "hemlo world"

Curly brackets can also be used instead of "do ... end" on blocks, as "{ ... }".

Another case where you can see square brackets or curly brackets used - is in the special initializers where any symbol can be used, like:

%w{ hello world } # => ["hello","world"]
%w[ hello world ] # => ["hello","world"]
%r{ hello world } # => / hello world /
%r[ hello world ] # => / hello world /
%q{ hello world } # => "hello world"
%q[ hello world ] # => "hello world"
%q| hello world | # => "hello world"