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lib/types: Introduce lazyAttrsOf

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The standard attrsOf is strict in its *values*, meaning it's impossible to
access only one attribute value without evaluating all others as well.
lazyAttrsOf is a version that doesn't have that problem, at the expense
of conditional definitions not properly working anymore.
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Silvan Mosberger 2019-10-12 21:18:53 +02:00 • committed by Silvan Mosberger
parent 4268b4f9cf
commit b48717d1eb
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24
lib/types.nix
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@ -302,6 +302,30 @@ rec {
functor = (defaultFunctor name) // { wrapped = elemType; };
};
# A version of attrsOf that's lazy in its values at the expense of
# conditional definitions not working properly. E.g. defining a value with
# `foo.attr = mkIf false 10`, then `foo ? attr == true`, whereas with
# attrsOf it would correctly be `false`. Accessing `foo.attr` would throw an
# error that it's not defined. Use only if conditional definitions don't make sense.
lazyAttrsOf = elemType: mkOptionType rec {
name = "lazyAttrsOf";
description = "lazy attribute set of ${elemType.description}s";
check = isAttrs;
merge = loc: defs:
zipAttrsWith (name: defs:
let merged = mergeDefinitions (loc ++ [name]) elemType defs;
# mergedValue will trigger an appropriate error when accessed
in merged.optionalValue.value or elemType.emptyValue.value or merged.mergedValue
)
# Push down position info.
(map (def: mapAttrs (n: v: { inherit (def) file; value = v; }) def.value) defs);
emptyValue = { value = {}; };
getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<name>"]);
getSubModules = elemType.getSubModules;
substSubModules = m: lazyAttrsOf (elemType.substSubModules m);
functor = (defaultFunctor name) // { wrapped = elemType; };
};
# List or attribute set of ...
loaOf = elemType:
let