> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/sidef-lang/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/sidef-lang/syntax_and_semantics/constructs/given_when.md).

# Given/When

The `given/when` construct is borrowed from Raku and it's somewhat equivalent with `switch/case` from other languages.

```ruby
given (42) {
  case (_ < 0) {
       say "Negative value!"
  }
  when (0) {
       say "Null value!"
  }
  when (1) {
       say "Value is: 1"
  }
  default {
       say "Value is greater than 1!"
  }
}
```

* `case` is used to test an expression for trueness
* `when` is used to test a value using the rules of the smartmarch operator

The rules of the smartmarch operator are pretty simple:

* `Obj ~~ Obj` will always check for equality when both objects have the same type.
* `Obj ~~ Array` will return true if `Obj` exists inside the array.
* `Obj ~~ Hash` will return true when `Obj` is a key inside the hash.
* `Obj ~~ Regex` will try to match the `Obj` against the regex and returns true on a successful match.