How to find the definition of an existing method?

Question

I am new to programming and Ruby both. In some existing code, it says something like this:

kid_raising_btn=query("switch marked:'KIDRAISING'",:isOn).first

From this, I understand that a variable kid_raising_btn is defined, which will query and return true or false, then call the method first (but this is confusing).

How can I find what first does?

Answer 1

".first" is kind of convenient method. Answer for the UI query comes as an array. So the ".first" represent the first element of the array. There are few methods like ".count"

Ex: your Query :

ans = query("button",:accessibilityLabel)

Assume You will get result like this

[
    [0] "icon rewards new",
    [1] "icon my receipts new",
    [2] "icon my account",
    [3] "icon order@2x",
    [4] "icon check in"
]

if you use ".first" like this

ans2 = query("button",:accessibilityLabel).first

you will get a String with first element as a result instead of an array.

"icon rewards new"

Now you can see you get the first element as the answer

Answer 2

From your description, it sounds like the method chaining here might be contributing to your confusion, so first let's rewrite that line of code like this:

    query_response = query("switch marked: 'KIDRAISING'", :isOn)
    kid_raising_btn = query_response.first

Now, it's easier to see that the #query method returns an object that has a #first method. You can take a look at this object to see what class it is (query_response.class), and then either look up the appropriate documentation for the class or find the method definition in your codebase. For example, if #query returns an array, you can find the documentation here: http://ruby-doc.org/core-2.0.0/Array.html#method-i-first