trying to understand specific bit of ruby syntax

Question

I'm new to both Ruby and Rails, and as I go over various tutorials, I occasionally hit on a bit of Ruby syntax that I just can't grok.

For instance, what does this actually do?

root to: "welcome#index"

I can gather that this is probably a method named "root", but I'm lost after that. "To" isn't a symbol, is it? The colon would be before, as in ":to" if it were. Is this some form of keyword argument utilizing hashes? I can't make this syntax work when trying it in irb with ruby1.9.3.

I know this might be a RTFM question, but I can't even think of what to google for this.

Thanks!

I'm still playing around with this syntax,

def func(h)
    puts h[:to]
end

x = { :to => "welcome#index" }
y = :to => "welcome#index"
z = to: "welcome#index" 

func to: "welcome#index"

I see that this example only works with the lines defining "y" and "z" commented out. So the braceless and the "colon-after" syntax are only valid in the context of calling a method?

Answer 1

First, that's right - root is a method call. Now

to: 'welcome#index' 

is equivalent to

:to => 'welcome#index'

and it's a Hash where the key is :to symbol and value is 'welcome#index' string. You can use this syntax in defining hashes since Ruby 1.9.

Answer 2

It's equivalent to

root(:to => "welcome#index")

I'm having trouble finding the official documentation on the new hash syntax, but when you see foo: bar, it means that foo is a symbol used as a key in the hash and has a value bar.