I encountered this string that looks like JSON syntax but I've never seen a property with a colon before it and not with a backwards greater than or equals sign:

Badge {

Is it a JSON string and if so what does the colon do?

  • I think that's Ruby. Where did you find the code? – Gregory Nisbet Apr 9 '19 at 1:20
  • It was output to the console during an upgrade of Discourse – 1.21 gigawatts Apr 9 '19 at 1:43
  • github.com/discourse/discourse ... Discourse is about 65% ruby by weight (according to GitHub). – Gregory Nisbet Apr 9 '19 at 1:45
  • 1
    Badge is the name of the class. I updated my answer with a link to the file that defines the class. The hash literal is valid Ruby, but a human would be more likely to use the key: value syntax. – Gregory Nisbet Apr 9 '19 at 1:51


Knowing more about the context (message written to console during an updgrade of discourse), you likely saw an instance of this class being printed.

I think you are looking at Ruby code, although it is strange to mix symbol literals and =>.

  • An identifier beginning with a colon is a :symbol literal.
  • A key-value pair in a hash table can be written key => value or key: value, but the latter syntax only works with symbol literals.
  • Badge doesn't have parentheses after it and you can omit parentheses.

Some other languages use => to separate key value pairs, here's why the other likely suspects don't fit.

  • Perl: A key begining with : must be quoted. Bare identifiers and bare identifiers with a leading - are the only things that do not need to be quoted in Perl in this context.
  • PHP: PHP allows {} for accessing array values $a{6}, but does not allow braces for array literals. Also, you can't leave the parentheses off a function call in PHP.

Colon variable refers to :abc type variables you might have seen in Ruby. They are called Ruby symbols.

A Ruby symbol is not a variable because it cannot be assigned a value.

Also, a Ruby symbol is not a reference to another variable nor is it a pointer to a memory location.

Still a symbol has a value and whenever the name of the symbol is same, its value is the same.

An example will make it more clear.

# It is trivial to assign a value to a variable.
abc = "1"
=> "1"

# But a symbol cannot be assigned any value.
:a = "1"
# SyntaxError: A symbol cannot be assigned a value

# Can use a variable as a map-key 
m = {abc => "1"}
=> {"1"=>"1"}

# Can use a string as a map-key 
=> {"def"=>"1"}

# Can also use a symbol as a map-key 
m = {:a => "1"}
=> {:a=>"1"}

# Can use same symbol as key in another map
m2 = {:a => "2"}
=> {:a=>"2"}

# And it won't affect the previous map.
=> {:a=>"1"}

=> {:a=>"2"}
  • So is a symbol comparable to a constant? – 1.21 gigawatts Apr 12 '19 at 23:37
  • No, a symbol in Ruby is comparable to a symbol in Lisp or in Scala. A Ruby symbol is a datatype that represents the concept of a "name" or a "label", just like a Ruby string represents the concept of "text" or a Ruby integer represents the concept of, well, "integer". – Jörg W Mittag Sep 11 '20 at 4:46

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