Ruby on Rails: what does "equals" symbol mean as a parameter?

Question

Some open source I've been using has the below line as a function declaration:

def parse_query(query=nil, options={}, models=nil)

What effect do the "equals" symbols have on the statement? Does it just make the parameters optional?

Answer 1

It sets the default value of the parameter, if the person calling the function does not specify one.

Answer 2

Similar to Python and C++, the equals sign in the parameter list lets you specify a default parameter. For example, in Python:

def hello_world(message="Hello World"):
    print "message = "+message

Calling this function like this:

hello_world()

Will result in:

message = Hello World

But calling the function like this:

hello_world("changed default")

results in:

message = changed default