Today I Learned

A Hashrocket project

Use assigned variables on its own assign statement

Javascript allows you to use an assigned variables into the same assignment statement. This is a non expected behavior for me as the first languages I’ve learned were compiled languages and that would fail compilation, at least on the ones I’ve experienced with.

Here’s an example:

Javascript ES2015:

const [hello, world] = [
  () => `Hello ${world()}`,
  () => "World",
]
hello()
//=> "Hello World"

In this example I’m assigning the second function into the world variable by using destructuring assignment and I’m using this by calling world() in the first function.

Ruby:

To my surprise ruby allows the same behavior:

hello, world = [
  lambda { "Hello #{world.call}" },
  lambda { "World" },
]
hello.call
#=> "Hello World"

Elixir:

Well, Elixir will act as I previously expected, so assigned variables are allowed to be used only after the statement that creates them.

[hello, world] = [
  fn -> "Hello #{world.()}" end,
  fn -> "World" end,
]
hello.()
#=> ERROR** (CompileError) iex:2: undefined function world/0

I won’t start using this approach, but it’s important to know that’s possible.

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