longestValidPathPrefix
lib.attrsets.longestValidPathPrefix
Docs pulled from | This Revision | about 1 hour ago
Return the longest prefix of an attribute path that refers to an existing attribute in a nesting of attribute sets.
Can be used after mapAttrsRecursiveCond
to apply a condition,
although this will evaluate the predicate function on sibling attributes as well.
Note that the empty attribute path is valid for all values, so this function only throws an exception if any of its inputs does.
Laws:
-
attrsets.longestValidPathPrefix [] x == []
-
hasAttrByPath (attrsets.longestValidPathPrefix p x) x == true
Inputs
attrPath
-
A list of strings representing the longest possible path that may be returned.
v
-
The nested attribute set to check.
Type
attrsets.longestValidPathPrefix :: [String] -> Value -> [String]
Examples
lib.attrsets.longestValidPathPrefix
usage example
x = { a = { b = 3; }; }
attrsets.longestValidPathPrefix ["a" "b" "c"] x
=> ["a" "b"]
attrsets.longestValidPathPrefix ["a"] x
=> ["a"]
attrsets.longestValidPathPrefix ["z" "z"] x
=> []
attrsets.longestValidPathPrefix ["z" "z"] (throw "no need")
=> []
Noogle detected
Implementation
The following is the current implementation of this function.
longestValidPathPrefix =
attrPath:
v:
let
lenAttrPath = length attrPath;
getPrefixForSetAtIndex =
# The nested attribute set to check, if it is an attribute set, which
# is not a given.
remainingSet:
# The index of the attribute we're about to check, as well as
# the length of the prefix we've already checked.
remainingPathIndex:
if remainingPathIndex == lenAttrPath then
# All previously checked attributes exist, and no attr names left,
# so we return the whole path.
attrPath
else
let
attr = elemAt attrPath remainingPathIndex;
in
if remainingSet ? ${attr} then
getPrefixForSetAtIndex
remainingSet.${attr} # advance from the set to the attribute value
(remainingPathIndex + 1) # advance the path
else
# The attribute doesn't exist, so we return the prefix up to the
# previously checked length.
take remainingPathIndex attrPath;
in
getPrefixForSetAtIndex v 0;