diff options
author | Alyssa Ross <hi@alyssa.is> | 2023-12-15 19:32:38 +0100 |
---|---|---|
committer | Alyssa Ross <hi@alyssa.is> | 2023-12-15 19:32:38 +0100 |
commit | 6b8e2555ef013b579cda57025b17d662e0f1fe1f (patch) | |
tree | 5a83c673af26c9976acd5a5dfa20e09e06898047 /nixpkgs/lib/attrsets.nix | |
parent | 66ca7a150b5c051f0728f13134e6265cc46f370c (diff) | |
parent | 02357adddd0889782362d999628de9d309d202dc (diff) | |
download | nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.tar nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.tar.gz nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.tar.bz2 nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.tar.lz nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.tar.xz nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.tar.zst nixlib-6b8e2555ef013b579cda57025b17d662e0f1fe1f.zip |
Merge branch 'nixos-unstable-small' of https://github.com/NixOS/nixpkgs
Diffstat (limited to 'nixpkgs/lib/attrsets.nix')
-rw-r--r-- | nixpkgs/lib/attrsets.nix | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/nixpkgs/lib/attrsets.nix b/nixpkgs/lib/attrsets.nix index 3d4366ce1814..99b686918453 100644 --- a/nixpkgs/lib/attrsets.nix +++ b/nixpkgs/lib/attrsets.nix @@ -14,6 +14,14 @@ rec { /* Return an attribute from nested attribute sets. + Nix has an [attribute selection operator `. or`](https://nixos.org/manual/nix/stable/language/operators#attribute-selection) which is sufficient for such queries, as long as the number of attributes is static. For example: + + ```nix + (x.a.b or 6) == attrByPath ["a" "b"] 6 x + # and + (x.${f p}."example.com" or 6) == attrByPath [ (f p) "example.com" ] 6 x + ``` + Example: x = { a = { b = 3; }; } # ["a" "b"] is equivalent to x.a.b @@ -51,12 +59,27 @@ rec { /* Return if an attribute from nested attribute set exists. + Nix has a [has attribute operator `?`](https://nixos.org/manual/nix/stable/language/operators#has-attribute), which is sufficient for such queries, as long as the number of attributes is static. For example: + + ```nix + (x?a.b) == hasAttryByPath ["a" "b"] x + # and + (x?${f p}."example.com") == hasAttryByPath [ (f p) "example.com" ] x + ``` + + **Laws**: + 1. ```nix + hasAttrByPath [] x == true + ``` + Example: x = { a = { b = 3; }; } hasAttrByPath ["a" "b"] x => true hasAttrByPath ["z" "z"] x => false + hasAttrByPath [] (throw "no need") + => true Type: hasAttrByPath :: [String] -> AttrSet -> Bool @@ -80,6 +103,71 @@ rec { in hasAttrByPath' 0 e; + /* + 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`](#function-library-lib.attrsets.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**: + 1. ```nix + attrsets.longestValidPathPrefix [] x == [] + ``` + + 2. ```nix + hasAttrByPath (attrsets.longestValidPathPrefix p x) x == true + ``` + + 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") + => [] + + Type: + attrsets.longestValidPathPrefix :: [String] -> Value -> [String] + */ + longestValidPathPrefix = + # A list of strings representing the longest possible path that may be returned. + attrPath: + # The nested attribute set to check. + 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; + /* Create a new attribute set with `value` set at the nested attribute location specified in `attrPath`. Example: @@ -105,6 +193,14 @@ rec { /* Like `attrByPath`, but without a default value. If it doesn't find the path it will throw an error. + Nix has an [attribute selection operator](https://nixos.org/manual/nix/stable/language/operators#attribute-selection) which is sufficient for such queries, as long as the number of attributes is static. For example: + + ```nix + x.a.b == getAttrByPath ["a" "b"] x + # and + x.${f p}."example.com" == getAttrByPath [ (f p) "example.com" ] x + ``` + Example: x = { a = { b = 3; }; } getAttrFromPath ["a" "b"] x |