CODEWITHSUNDEEP
jsonnet
svenwltr
svenwltr

Reputation: 18482

How to use local variables in arrays?

I want to write a function that returns an array. The array contains objects, where some of them need to reuse a certain object (metadata in this example). This object depends on a parameter of the function and repeating it would be a bit cumbersome.

I tried this:

local fn(name) = [
    local metadata = { name: name };
    { metadata: metadata, value: "foo" },
    { metadata: metadata, value: "bar" },
];

fn("blub")

Unfortunately I get this error:

STATIC ERROR: example.jsonnet:4:17-24: Unknown variable: metadata

I would expect that metadata is also available within the second item. Is there a way to solve this without repeating metadata and without having the function return an object?

Upvotes: 2

Views: 2124

Answers (2)

sbarzowski
sbarzowski

Reputation: 2991

When you have local foo = expr1; expr2, foo is defined only in expr2. So in the example you provided metadata is visible only in the first element of the array. And local is just an expression. You can use it anywhere in the code where an expression is expected, e.g. 42 + (local x = 17 - 3; x + 4). The local in Jsonnet is an analog of let ... in ... from Haskell/Ocaml etc.

The solution is to define metadata for the whole array expression, like in the OP's answer.

Upvotes: 3

svenwltr
svenwltr

Reputation: 18482

I just saw that the documentation actually provides an answer for this:

local fn(name) =
    local metadata = { name: name };
    [
        { metadata: metadata, value: "foo" },
        { metadata: metadata, value: "bar" },
    ];

fn("blub")

Upvotes: 0

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