CODEWITHSUNDEEP
ruby-on-railsrubyexpression
Lawleyenda
Lawleyenda

Reputation: 75

Ruby Intro to Parallel Assignments

a = [1, 2, 3, 4]

b,  c = 99, *a   → b == 99, c == 1
b, *c = 99, *a   → b == 99, c == [1, 2, 3, 4]

Can someone please throughly explained why in Ruby the asterisk makes the code return what it returns? I understand that the if an lvalue has an asterisk, it assigns rvalues to that lvalues. However, why does '*a' make 'c' return only the '1' value in the array and why does '*a' and '*c' cancel each other out?

Upvotes: 0

Views: 52

Answers (1)

mikej
mikej

Reputation: 66263

In both cases, 99, *a on the right-hand side expands into the array [99, 1, 2, 3, 4]

In 

b,  c = 99, *a

b and c become the first two values of the array, with the rest of the array discarded.

In

b, *c = 99, *a

b becomes the first value from the array and c is assigned the rest (because of the splat on the left-hand side).

The 99, *a on the right-hand side is an example of where the square brackets around an array are optional in an assignment.

A simpler example:

a = 1, 2, 3 → a == [1, 2, 3]

Or a more explicit version of your example:

example = [99, *a] → example == [99, 1, 2, 3, 4]

Upvotes: 4

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