init: lib.foldlAttrs (15a8d05b) · Commits · nix / nixpkgs

lib/attrsets.nix

+60 −0

Original line number	Diff line number	Diff line
		@@ -333,6 +333,66 @@ rec {
		) (attrNames set)
		);

		/*
		Like builtins.foldl' but for attribute sets.
		Iterates over every name-value pair in the given attribute set.
		The result of the callback function is often called `acc` for accumulator. It is passed between callbacks from left to right and the final `acc` is the return value of `foldlAttrs`.

		Attention:
		There is a completely different function
		`lib.foldAttrs`
		which has nothing to do with this function, despite the similar name.

		Example:
		foldlAttrs
		(acc: name: value: {
		sum = acc.sum + value;
		names = acc.names ++ [name];
		})
		{ sum = 0; names = []; }
		{
		foo = 1;
		bar = 10;
		}
		->
		{
		sum = 11;
		names = ["bar" "foo"];
		}

		foldlAttrs
		(throw "function not needed")
		123
		{};
		->
		123

		foldlAttrs
		(_: _: v: v)
		(throw "initial accumulator not needed")
		{ z = 3; a = 2; };
		->
		3

		The accumulator doesn't have to be an attrset.
		It can be as simple as a number or string.

		foldlAttrs
		(acc: _: v: acc * 10 + v)
		1
		{ z = 1; a = 2; };
		->
		121

		Type:
		foldlAttrs :: ( a -> String -> b -> a ) -> a -> { ... :: b } -> a
		*/
		foldlAttrs = f: init: set:
		foldl'
		(acc: name: f acc name set.${name})
		init
		(attrNames set);

		/* Apply fold functions to values grouped by key.

		Example:

+1 −1

Original line number	Diff line number	Diff line
		@@ -78,7 +78,7 @@ let
		composeManyExtensions makeExtensible makeExtensibleWithCustomName;
		inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath
		getAttrFromPath attrVals attrValues getAttrs catAttrs filterAttrs
		filterAttrsRecursive foldAttrs collect nameValuePair mapAttrs
		filterAttrsRecursive foldlAttrs foldAttrs collect nameValuePair mapAttrs
		mapAttrs' mapAttrsToList concatMapAttrs mapAttrsRecursive mapAttrsRecursiveCond
		genAttrs isDerivation toDerivation optionalAttrs
		zipAttrsWithNames zipAttrsWith zipAttrs recursiveUpdateUntil

+31 −0

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		@@ -533,6 +533,37 @@ runTests {
		};
		};

		# code from example
		testFoldlAttrs = {
		expr = {
		example = foldlAttrs
		(acc: name: value: {
		sum = acc.sum + value;
		names = acc.names ++ [ name ];
		})
		{ sum = 0; names = [ ]; }
		{
		foo = 1;
		bar = 10;
		};
		# should just return the initial value
		emptySet = foldlAttrs (throw "function not needed") 123 { };
		# should just evaluate to the last value
		accNotNeeded = foldlAttrs (_acc: _name: v: v) (throw "accumulator not needed") { z = 3; a = 2; };
		# the accumulator doesnt have to be an attrset it can be as trivial as being just a number or string
		trivialAcc = foldlAttrs (acc: _name: v: acc * 10 + v) 1 { z = 1; a = 2; };
		};
		expected = {
		example = {
		sum = 11;
		names = [ "bar" "foo" ];
		};
		emptySet = 123;
		accNotNeeded = 3;
		trivialAcc = 121;
		};
		};

		# code from the example
		testRecursiveUpdateUntil = {
		expr = recursiveUpdateUntil (path: l: r: path == ["foo"]) {