What's the difference between Ruby Core API and Standard Library API?

Question

Ruby Doc has two sections: Core and Standard. Core comes by default and standard has additional libraries/methods etc. Does it mean I have to `require` these standard libraries in order to use them? I thought so and picked `DateTime.now` from standard library without requiring anything, and it worked.

Accepted Answer

Yep, you got it right. Core functionality is everything you don't have to `require` to use.

`DateTime` seems to be not in the core (are you running your line inside of rails console, maybe?)

```
DateTime.now # => 
# ~> -:1:in `<main>': uninitialized constant DateTime (NameError)
```

But `Time` is

```
Time # => Time
Time.now # => 2013-08-29 12:32:54 +0400
```

Only a few methods of `Time` are in core, though. To get more functionality (like `Time.parse`) you have to

```
require 'time'
```

What's the difference between Ruby Core API and Standard Library API?

Solution

Problem