lib.attrsets.hasAttrByPath

Return if an attribute from nested attribute set exists.

Nix has a has attribute operator ?, which is sufficient for such queries, as long as the number of attributes is static. For example:

(x?a.b) == hasAttrByPath ["a" "b"] x
# and
(x?${f p}."example.com") == hasAttrByPath [ (f p) "example.com" ] x

Laws:

1. hasAttrByPath [] x == true
   

Inputs

attrPath

A list of strings representing the attribute path to check from set

e

The nested attribute set to check

Type

hasAttrByPath :: [String] -> AttrSet -> Bool

Examples

x = { a = { b = 3; }; }
hasAttrByPath ["a" "b"] x
=> true
hasAttrByPath ["z" "z"] x
=> false
hasAttrByPath [] (throw "no need")
=> true

Noogle detected

• lib.hasAttrByPath

hasAttrByPath =
    attrPath:
    e:
    let
      lenAttrPath = length attrPath;
      hasAttrByPath' = n: s: (
        n == lenAttrPath || (
          let
            attr = elemAt attrPath n;
          in
          if s ? ${attr} then hasAttrByPath' (n + 1) s.${attr}
          else false
        )
      );
    in
      hasAttrByPath' 0 e;