···
1
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<section xmlns="http://docbook.org/ns/docbook"
2
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xmlns:xlink="http://www.w3.org/1999/xlink"
3
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xmlns:xi="http://www.w3.org/2001/XInclude"
4
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xml:id="sec-functions-library-attrset">
5
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<title>Attribute-Set Functions</title>
7
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<section xml:id="function-library-lib.attrsets.attrByPath">
8
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<title><function>lib.attrset.attrByPath</function></title>
10
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<subtitle><literal>attrByPath :: [String] -> Any -> AttrSet -> Any</literal>
13
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<xi:include href="./locations.xml" xpointer="lib.attrsets.attrByPath" />
16
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Return an attribute from within nested attribute sets.
22
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<varname>attrPath</varname>
26
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A list of strings representing the path through the nested attribute set <varname>set</varname>.
32
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<varname>default</varname>
36
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Default value if <varname>attrPath</varname> does not resolve to an existing value.
42
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<varname>set</varname>
46
-
The nested attributeset to select values from.
52
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<example xml:id="function-library-lib.attrset.attrByPath-example-value-exists">
53
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<title>Extracting a value from a nested attribute set</title>
54
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<programlisting><![CDATA[
55
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let set = { a = { b = 3; }; };
56
-
in lib.attrsets.attrByPath [ "a" "b" ] 0 set
58
-
]]></programlisting>
61
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<example xml:id="function-library-lib.attrset.attrByPath-example-default-value">
62
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<title>No value at the path, instead using the default</title>
63
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<programlisting><![CDATA[
64
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lib.attrsets.attrByPath [ "a" "b" ] 0 {}
66
-
]]></programlisting>
70
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<section xml:id="function-library-lib.attrsets.hasAttrByPath">
71
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<title><function>lib.attrsets.hasAttrByPath</function></title>
73
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<subtitle><literal>hasAttrByPath :: [String] -> AttrSet -> Bool</literal>
76
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<xi:include href="./locations.xml" xpointer="lib.attrsets.hasAttrByPath" />
79
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Determine if an attribute exists within a nested attribute set.
85
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<varname>attrPath</varname>
89
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A list of strings representing the path through the nested attribute set <varname>set</varname>.
95
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<varname>set</varname>
99
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The nested attributeset to check.
105
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<example xml:id="function-library-lib.attrsets.hasAttrByPath-example">
106
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<title>A nested value does exist inside a set</title>
107
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<programlisting><![CDATA[
108
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lib.attrsets.hasAttrByPath
109
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[ "a" "b" "c" "d" ]
110
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{ a = { b = { c = { d = 123; }; }; }; }
112
-
]]></programlisting>
116
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<section xml:id="function-library-lib.attrsets.setAttrByPath">
117
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<title><function>lib.attrsets.setAttrByPath</function></title>
119
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<subtitle><literal>setAttrByPath :: [String] -> Any -> AttrSet</literal>
122
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<xi:include href="./locations.xml" xpointer="lib.attrsets.setAttrByPath" />
125
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Create a new attribute set with <varname>value</varname> set at the nested attribute location specified in <varname>attrPath</varname>.
131
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<varname>attrPath</varname>
135
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A list of strings representing the path through the nested attribute set.
141
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<varname>value</varname>
145
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The value to set at the location described by <varname>attrPath</varname>.
151
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<example xml:id="function-library-lib.attrsets.setAttrByPath-example">
152
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<title>Creating a new nested attribute set</title>
153
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<programlisting><![CDATA[
154
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lib.attrsets.setAttrByPath [ "a" "b" ] 3
155
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=> { a = { b = 3; }; }
156
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]]></programlisting>
160
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<section xml:id="function-library-lib.attrsets.getAttrFromPath">
161
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<title><function>lib.attrsets.getAttrFromPath</function></title>
163
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<subtitle><literal>getAttrFromPath :: [String] -> AttrSet -> Value</literal>
166
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<xi:include href="./locations.xml" xpointer="lib.attrsets.getAttrFromPath" />
169
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Like <xref linkend="function-library-lib.attrsets.attrByPath" /> except without a default, and it will throw if the value doesn't exist.
175
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<varname>attrPath</varname>
179
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A list of strings representing the path through the nested attribute set <varname>set</varname>.
185
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<varname>set</varname>
189
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The nested attribute set to find the value in.
195
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<example xml:id="function-library-lib.attrsets.getAttrPath-example-success">
196
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<title>Succesfully getting a value from an attribute set</title>
197
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<programlisting><![CDATA[
198
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lib.attrsets.getAttrFromPath [ "a" "b" ] { a = { b = 3; }; }
200
-
]]></programlisting>
203
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<example xml:id="function-library-lib.attrsets.getAttrPath-example-throw">
204
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<title>Throwing after failing to get a value from an attribute set</title>
205
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<programlisting><![CDATA[
206
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lib.attrsets.getAttrFromPath [ "x" "y" ] { }
207
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=> error: cannot find attribute `x.y'
208
-
]]></programlisting>
212
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<section xml:id="function-library-lib.attrsets.attrVals">
213
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<title><function>lib.attrsets.attrVals</function></title>
215
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<subtitle><literal>attrVals :: [String] -> AttrSet -> [Any]</literal>
218
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<xi:include href="./locations.xml" xpointer="lib.attrsets.attrVals" />
221
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Return the specified attributes from a set. All values must exist.
227
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<varname>nameList</varname>
231
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The list of attributes to fetch from <varname>set</varname>. Each attribute name must exist on the attrbitue set.
237
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<varname>set</varname>
241
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The set to get attribute values from.
247
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<example xml:id="function-library-lib.attrsets.attrVals-example-success">
248
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<title>Getting several values from an attribute set</title>
249
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<programlisting><![CDATA[
250
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lib.attrsets.attrVals [ "a" "b" "c" ] { a = 1; b = 2; c = 3; }
252
-
]]></programlisting>
255
-
<example xml:id="function-library-lib.attrsets.attrVals-failure">
256
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<title>Getting missing values from an attribute set</title>
257
-
<programlisting><![CDATA[
258
-
lib.attrsets.attrVals [ "d" ] { }
259
-
error: attribute 'd' missing
260
-
]]></programlisting>
264
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<section xml:id="function-library-lib.attrsets.attrValues">
265
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<title><function>lib.attrsets.attrValues</function></title>
267
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<subtitle><literal>attrValues :: AttrSet -> [Any]</literal>
270
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.attrValues" />
273
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Get all the attribute values from an attribute set.
277
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Provides a backwards-compatible interface of <function>builtins.attrValues</function> for Nix version older than 1.8.
283
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<varname>attrs</varname>
293
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<example xml:id="function-library-lib.attrsets.attrValues-example">
295
-
<programlisting><![CDATA[
296
-
lib.attrsets.attrValues { a = 1; b = 2; c = 3; }
298
-
]]></programlisting>
302
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<section xml:id="function-library-lib.attrsets.catAttrs">
303
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<title><function>lib.attrsets.catAttrs</function></title>
305
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<subtitle><literal>catAttrs :: String -> [AttrSet] -> [Any]</literal>
308
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.catAttrs" />
311
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Collect each attribute named `attr' from the list of attribute sets, <varname>sets</varname>. Sets that don't contain the named attribute are ignored.
315
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Provides a backwards-compatible interface of <function>builtins.catAttrs</function> for Nix version older than 1.9.
321
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<varname>attr</varname>
325
-
Attribute name to select from each attribute set in <varname>sets</varname>.
331
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<varname>sets</varname>
335
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The list of attribute sets to select <varname>attr</varname> from.
341
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<example xml:id="function-library-lib.attrsets.catAttrs-example">
342
-
<title>Collect an attribute from a list of attribute sets.</title>
344
-
Attribute sets which don't have the attribute are ignored.
346
-
<programlisting><![CDATA[
347
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catAttrs "a" [{a = 1;} {b = 0;} {a = 2;}]
349
-
]]></programlisting>
353
-
<section xml:id="function-library-lib.attrsets.filterAttrs">
354
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<title><function>lib.attrsets.filterAttrs</function></title>
356
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<subtitle><literal>filterAttrs :: (String -> Any -> Bool) -> AttrSet -> AttrSet</literal>
359
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.filterAttrs" />
362
-
Filter an attribute set by removing all attributes for which the given predicate return false.
368
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<varname>pred</varname>
372
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<literal>String -> Any -> Bool</literal>
375
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Predicate which returns true to include an attribute, or returns false to exclude it.
380
-
<varname>name</varname>
384
-
The attribute's name
390
-
<varname>value</varname>
394
-
The attribute's value
400
-
Returns <literal>true</literal> to include the attribute, <literal>false</literal> to exclude the attribute.
406
-
<varname>set</varname>
410
-
The attribute set to filter
416
-
<example xml:id="function-library-lib.attrsets.filterAttrs-example">
417
-
<title>Filtering an attributeset</title>
418
-
<programlisting><![CDATA[
419
-
filterAttrs (n: v: n == "foo") { foo = 1; bar = 2; }
421
-
]]></programlisting>
425
-
<section xml:id="function-library-lib.attrsets.filterAttrsRecursive">
426
-
<title><function>lib.attrsets.filterAttrsRecursive</function></title>
428
-
<subtitle><literal>filterAttrsRecursive :: (String -> Any -> Bool) -> AttrSet -> AttrSet</literal>
431
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.filterAttrsRecursive" />
434
-
Filter an attribute set recursively by removing all attributes for which the given predicate return false.
440
-
<varname>pred</varname>
444
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<literal>String -> Any -> Bool</literal>
447
-
Predicate which returns true to include an attribute, or returns false to exclude it.
452
-
<varname>name</varname>
456
-
The attribute's name
462
-
<varname>value</varname>
466
-
The attribute's value
472
-
Returns <literal>true</literal> to include the attribute, <literal>false</literal> to exclude the attribute.
478
-
<varname>set</varname>
482
-
The attribute set to filter
488
-
<example xml:id="function-library-lib.attrsets.filterAttrsRecursive-example">
489
-
<title>Recursively filtering an attribute set</title>
490
-
<programlisting><![CDATA[
491
-
lib.attrsets.filterAttrsRecursive
498
-
this-one-is-present = {
499
-
this-is-excluded = null;
502
-
this-one-is-also-excluded = null;
504
-
also-excluded = null;
511
-
this-one-is-present = { };
515
-
]]></programlisting>
519
-
<section xml:id="function-library-lib.attrsets.foldAttrs">
520
-
<title><function>lib.attrsets.foldAttrs</function></title>
522
-
<subtitle><literal>foldAttrs :: (Any -> Any -> Any) -> Any -> [AttrSets] -> Any</literal>
525
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.foldAttrs" />
528
-
Apply fold function to values grouped by key.
534
-
<varname>op</varname>
538
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<literal>Any -> Any -> Any</literal>
541
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Given a value <varname>val</varname> and a collector <varname>col</varname>, combine the two.
546
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<varname>val</varname>
550
-
An attribute's value
556
-
<varname>col</varname>
559
-
<!-- TODO: make this not bad, use more fold-ey terms -->
561
-
The result of previous <function>op</function> calls with other values and <function>nul</function>.
570
-
<varname>nul</varname>
574
-
The null-value, the starting value.
580
-
<varname>list_of_attrs</varname>
584
-
A list of attribute sets to fold together by key.
590
-
<example xml:id="function-library-lib.attrsets.foldAttrs-example">
591
-
<title>Combining an attribute of lists in to one attribute set</title>
592
-
<programlisting><![CDATA[
593
-
lib.attrsets.foldAttrs
594
-
(n: a: [n] ++ a) []
600
-
=> { a = [ 2 3 ]; b = [ 7 6 ]; }
601
-
]]></programlisting>
605
-
<section xml:id="function-library-lib.attrsets.collect">
606
-
<title><function>lib.attrsets.collect</function></title>
608
-
<subtitle><literal>collect :: (Any -> Bool) -> AttrSet -> [Any]</literal>
611
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.collect" />
614
-
Recursively collect sets that verify a given predicate named <varname>pred</varname> from the set <varname>attrs</varname>. The recursion stops when <varname>pred</varname> returns <literal>true</literal>.
620
-
<varname>pred</varname>
624
-
<literal>Any -> Bool</literal>
627
-
Given an attribute's value, determine if recursion should stop.
632
-
<varname>value</varname>
636
-
The attribute set value.
645
-
<varname>attrs</varname>
649
-
The attribute set to recursively collect.
655
-
<example xml:id="function-library-lib.attrsets.collect-example-lists">
656
-
<title>Collecting all lists from an attribute set</title>
657
-
<programlisting><![CDATA[
658
-
lib.attrsets.collect isList { a = { b = ["b"]; }; c = [1]; }
660
-
]]></programlisting>
663
-
<example xml:id="function-library-lib.attrsets.collect-example-outpath">
664
-
<title>Collecting all attribute-sets which contain the <literal>outPath</literal> attribute name.</title>
665
-
<programlisting><![CDATA[
666
-
collect (x: x ? outPath)
667
-
{ a = { outPath = "a/"; }; b = { outPath = "b/"; }; }
668
-
=> [{ outPath = "a/"; } { outPath = "b/"; }]
669
-
]]></programlisting>
673
-
<section xml:id="function-library-lib.attrsets.nameValuePair">
674
-
<title><function>lib.attrsets.nameValuePair</function></title>
676
-
<subtitle><literal>nameValuePair :: String -> Any -> AttrSet</literal>
679
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.nameValuePair" />
682
-
Utility function that creates a <literal>{name, value}</literal> pair as expected by <function>builtins.listToAttrs</function>.
688
-
<varname>name</varname>
692
-
The attribute name.
698
-
<varname>value</varname>
702
-
The attribute value.
708
-
<example xml:id="function-library-lib.attrsets.nameValuePair-example">
709
-
<title>Creating a name value pair</title>
710
-
<programlisting><![CDATA[
711
-
nameValuePair "some" 6
712
-
=> { name = "some"; value = 6; }
713
-
]]></programlisting>
717
-
<section xml:id="function-library-lib.attrsets.mapAttrs">
718
-
<title><function>lib.attrsets.mapAttrs</function></title>
720
-
<subtitle><literal></literal>
723
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.mapAttrs" />
726
-
Apply a function to each element in an attribute set, creating a new attribute set.
730
-
Provides a backwards-compatible interface of <function>builtins.mapAttrs</function> for Nix version older than 2.1.
736
-
<varname>fn</varname>
740
-
<literal>String -> Any -> Any</literal>
743
-
Given an attribute's name and value, return a new value.
748
-
<varname>name</varname>
752
-
The name of the attribute.
758
-
<varname>value</varname>
762
-
The attribute's value.
771
-
<example xml:id="function-library-lib.attrsets.mapAttrs-example">
772
-
<title>Modifying each value of an attribute set</title>
773
-
<programlisting><![CDATA[
774
-
lib.attrsets.mapAttrs
775
-
(name: value: name + "-" + value)
776
-
{ x = "foo"; y = "bar"; }
777
-
=> { x = "x-foo"; y = "y-bar"; }
778
-
]]></programlisting>
782
-
<section xml:id="function-library-lib.attrsets.mapAttrs-prime">
783
-
<title><function>lib.attrsets.mapAttrs'</function></title>
785
-
<subtitle><literal>mapAttrs' :: (String -> Any -> { name = String; value = Any }) -> AttrSet -> AttrSet</literal>
788
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.mapAttrs-prime" />
791
-
Like <function>mapAttrs</function>, but allows the name of each attribute to be changed in addition to the value. The applied function should return both the new name and value as a <function>nameValuePair</function>.
797
-
<varname>fn</varname>
801
-
<literal>String -> Any -> { name = String; value = Any }</literal>
804
-
Given an attribute's name and value, return a new <link
805
-
linkend="function-library-lib.attrsets.nameValuePair">name value pair</link>.
810
-
<varname>name</varname>
814
-
The name of the attribute.
820
-
<varname>value</varname>
824
-
The attribute's value.
833
-
<varname>set</varname>
837
-
The attribute set to map over.
843
-
<example xml:id="function-library-lib.attrsets.mapAttrs-prime-example">
844
-
<title>Change the name and value of each attribute of an attribute set</title>
845
-
<programlisting><![CDATA[
846
-
lib.attrsets.mapAttrs' (name: value: lib.attrsets.nameValuePair ("foo_" + name) ("bar-" + value))
847
-
{ x = "a"; y = "b"; }
848
-
=> { foo_x = "bar-a"; foo_y = "bar-b"; }
850
-
]]></programlisting>
854
-
<section xml:id="function-library-lib.attrsets.mapAttrsToList">
855
-
<title><function>lib.attrsets.mapAttrsToList</function></title>
857
-
<subtitle><literal>mapAttrsToList :: (String -> Any -> Any) ->
858
-
AttrSet -> [Any]</literal>
861
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.mapAttrsToList" />
864
-
Call <varname>fn</varname> for each attribute in the given <varname>set</varname> and return the result in a list.
870
-
<varname>fn</varname>
874
-
<literal>String -> Any -> Any</literal>
877
-
Given an attribute's name and value, return a new value.
882
-
<varname>name</varname>
886
-
The name of the attribute.
892
-
<varname>value</varname>
896
-
The attribute's value.
905
-
<varname>set</varname>
909
-
The attribute set to map over.
915
-
<example xml:id="function-library-lib.attrsets.mapAttrsToList-example">
916
-
<title>Combine attribute values and names in to a list</title>
917
-
<programlisting><![CDATA[
918
-
lib.attrsets.mapAttrsToList (name: value: "${name}=${value}")
919
-
{ x = "a"; y = "b"; }
921
-
]]></programlisting>
925
-
<section xml:id="function-library-lib.attrsets.mapAttrsRecursive">
926
-
<title><function>lib.attrsets.mapAttrsRecursive</function></title>
928
-
<subtitle><literal>mapAttrsRecursive :: ([String] > Any -> Any) -> AttrSet -> AttrSet</literal>
931
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.mapAttrsRecursive" />
934
-
Like <function>mapAttrs</function>, except that it recursively applies itself to attribute sets. Also, the first argument of the argument function is a <emphasis>list</emphasis> of the names of the containing attributes.
940
-
<varname>f</varname>
944
-
<literal>[ String ] -> Any -> Any</literal>
947
-
Given a list of attribute names and value, return a new value.
952
-
<varname>name_path</varname>
956
-
The list of attribute names to this value.
959
-
For example, the <varname>name_path</varname> for the <literal>example</literal> string in the attribute set <literal>{ foo = { bar = "example"; }; }</literal> is <literal>[ "foo" "bar" ]</literal>.
965
-
<varname>value</varname>
969
-
The attribute's value.
978
-
<varname>set</varname>
982
-
The attribute set to recursively map over.
988
-
<example xml:id="function-library-lib.attrsets.mapAttrsRecursive-example">
989
-
<title>A contrived example of using <function>lib.attrsets.mapAttrsRecursive</function></title>
990
-
<programlisting><![CDATA[
992
-
(path: value: concatStringsSep "-" (path ++ [value]))
1013
-
]]></programlisting>
1017
-
<section xml:id="function-library-lib.attrsets.mapAttrsRecursiveCond">
1018
-
<title><function>lib.attrsets.mapAttrsRecursiveCond</function></title>
1020
-
<subtitle><literal>mapAttrsRecursiveCond :: (AttrSet -> Bool) -> ([ String ] -> Any -> Any) -> AttrSet -> AttrSet</literal>
1023
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.mapAttrsRecursiveCond" />
1026
-
Like <function>mapAttrsRecursive</function>, but it takes an additional predicate function that tells it whether to recursive into an attribute set. If it returns false, <function>mapAttrsRecursiveCond</function> does not recurse, but does apply the map function. It is returns true, it does recurse, and does not apply the map function.
1032
-
<varname>cond</varname>
1036
-
<literal>(AttrSet -> Bool)</literal>
1039
-
Determine if <function>mapAttrsRecursive</function> should recurse deeper in to the attribute set.
1044
-
<varname>attributeset</varname>
1057
-
<varname>f</varname>
1061
-
<literal>[ String ] -> Any -> Any</literal>
1064
-
Given a list of attribute names and value, return a new value.
1069
-
<varname>name_path</varname>
1073
-
The list of attribute names to this value.
1076
-
For example, the <varname>name_path</varname> for the <literal>example</literal> string in the attribute set <literal>{ foo = { bar = "example"; }; }</literal> is <literal>[ "foo" "bar" ]</literal>.
1082
-
<varname>value</varname>
1086
-
The attribute's value.
1095
-
<varname>set</varname>
1099
-
The attribute set to recursively map over.
1105
-
<example xml:id="function-library-lib.attrsets.mapAttrsRecursiveCond-example">
1106
-
<title>Only convert attribute values to JSON if the containing attribute set is marked for recursion</title>
1107
-
<programlisting><![CDATA[
1108
-
lib.attrsets.mapAttrsRecursiveCond
1109
-
({ recurse ? false, ... }: recurse)
1110
-
(name: value: builtins.toJSON value)
1117
-
converted-to- = "json";
1122
-
hello = "\"there\"";
1125
-
dontrecur = "{\"converted-to\":\"json\"}";
1127
-
]]></programlisting>
1131
-
<section xml:id="function-library-lib.attrsets.genAttrs">
1132
-
<title><function>lib.attrsets.genAttrs</function></title>
1134
-
<subtitle><literal>genAttrs :: [ String ] -> (String -> Any) -> AttrSet</literal>
1137
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.genAttrs" />
1140
-
Generate an attribute set by mapping a function over a list of attribute names.
1146
-
<varname>names</varname>
1150
-
Names of values in the resulting attribute set.
1156
-
<varname>f</varname>
1160
-
<literal>String -> Any</literal>
1163
-
Takes the name of the attribute and return the attribute's value.
1168
-
<varname>name</varname>
1172
-
The name of the attribute to generate a value for.
1181
-
<example xml:id="function-library-lib.attrsets.genAttrs-example">
1182
-
<title>Generate an attrset based on names only</title>
1183
-
<programlisting><![CDATA[
1184
-
lib.attrsets.genAttrs [ "foo" "bar" ] (name: "x_${name}")
1185
-
=> { foo = "x_foo"; bar = "x_bar"; }
1186
-
]]></programlisting>
1190
-
<section xml:id="function-library-lib.attrsets.isDerivation">
1191
-
<title><function>lib.attrsets.isDerivation</function></title>
1193
-
<subtitle><literal>isDerivation :: Any -> Bool</literal>
1196
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.isDerivation" />
1199
-
Check whether the argument is a derivation. Any set with <code>{ type = "derivation"; }</code> counts as a derivation.
1205
-
<varname>value</varname>
1209
-
The value which is possibly a derivation.
1215
-
<example xml:id="function-library-lib.attrsets.isDerivation-example-true">
1216
-
<title>A package is a derivation</title>
1217
-
<programlisting><![CDATA[
1218
-
lib.attrsets.isDerivation (import <nixpkgs> {}).ruby
1220
-
]]></programlisting>
1223
-
<example xml:id="function-library-lib.attrsets.isDerivation-example-false">
1224
-
<title>Anything else is not a derivation</title>
1225
-
<programlisting><![CDATA[
1226
-
lib.attrsets.isDerivation "foobar"
1228
-
]]></programlisting>
1232
-
<section xml:id="function-library-lib.attrsets.toDerivation">
1233
-
<title><function>lib.attrsets.toDerivation</function></title>
1235
-
<subtitle><literal>toDerivation :: Path -> Derivation</literal>
1238
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.toDerivation" />
1241
-
Converts a store path to a fake derivation.
1247
-
<varname>path</varname>
1251
-
A store path to convert to a derivation.
1258
-
<section xml:id="function-library-lib.attrsets.optionalAttrs">
1259
-
<title><function>lib.attrsets.optionalAttrs</function></title>
1261
-
<subtitle><literal>optionalAttrs :: Bool -> AttrSet</literal>
1264
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.optionalAttrs" />
1267
-
Conditionally return an attribute set or an empty attribute set.
1273
-
<varname>cond</varname>
1277
-
Condition under which the <varname>as</varname> attribute set is returned.
1283
-
<varname>as</varname>
1287
-
The attribute set to return if <varname>cond</varname> is true.
1293
-
<example xml:id="function-library-lib.attrsets.optionalAttrs-example-true">
1294
-
<title>Return the provided attribute set when <varname>cond</varname> is true</title>
1295
-
<programlisting><![CDATA[
1296
-
lib.attrsets.optionalAttrs true { my = "set"; }
1297
-
=> { my = "set"; }
1298
-
]]></programlisting>
1301
-
<example xml:id="function-library-lib.attrsets.optionalAttrs-example-false">
1302
-
<title>Return an empty attribute set when <varname>cond</varname> is false</title>
1303
-
<programlisting><![CDATA[
1304
-
lib.attrsets.optionalAttrs false { my = "set"; }
1306
-
]]></programlisting>
1310
-
<section xml:id="function-library-lib.attrsets.zipAttrsWithNames">
1311
-
<title><function>lib.attrsets.zipAttrsWithNames</function></title>
1313
-
<subtitle><literal>zipAttrsWithNames :: [ String ] -> (String -> [ Any ] -> Any) -> [ AttrSet ] -> AttrSet</literal>
1316
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.zipAttrsWithNames" />
1319
-
Merge sets of attributes and use the function <varname>f</varname> to merge attribute values where the attribute name is in <varname>names</varname>.
1325
-
<varname>names</varname>
1329
-
A list of attribute names to zip.
1335
-
<varname>f</varname>
1339
-
<literal>(String -> [ Any ] -> Any</literal>
1342
-
Accepts an attribute name, all the values, and returns a combined value.
1347
-
<varname>name</varname>
1351
-
The name of the attribute each value came from.
1357
-
<varname>vs</varname>
1361
-
A list of values collected from the list of attribute sets.
1370
-
<varname>sets</varname>
1374
-
A list of attribute sets to zip together.
1380
-
<example xml:id="function-library-lib.attrsets.zipAttrsWithNames-example">
1381
-
<title>Summing a list of attribute sets of numbers</title>
1382
-
<programlisting><![CDATA[
1383
-
lib.attrsets.zipAttrsWithNames
1385
-
(name: vals: "${name} ${toString (builtins.foldl' (a: b: a + b) 0 vals)}")
1387
-
{ a = 1; b = 1; c = 1; }
1392
-
=> { a = "a 11"; b = "b 101"; }
1393
-
]]></programlisting>
1397
-
<section xml:id="function-library-lib.attrsets.zipAttrsWith">
1398
-
<title><function>lib.attrsets.zipAttrsWith</function></title>
1400
-
<subtitle><literal>zipAttrsWith :: (String -> [ Any ] -> Any) -> [ AttrSet ] -> AttrSet</literal>
1403
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.zipAttrsWith" />
1406
-
Merge sets of attributes and use the function <varname>f</varname> to merge attribute values. Similar to <xref
1407
-
linkend="function-library-lib.attrsets.zipAttrsWithNames" /> where all key names are passed for <varname>names</varname>.
1413
-
<varname>f</varname>
1417
-
<literal>(String -> [ Any ] -> Any</literal>
1420
-
Accepts an attribute name, all the values, and returns a combined value.
1425
-
<varname>name</varname>
1429
-
The name of the attribute each value came from.
1435
-
<varname>vs</varname>
1439
-
A list of values collected from the list of attribute sets.
1448
-
<varname>sets</varname>
1452
-
A list of attribute sets to zip together.
1458
-
<example xml:id="function-library-lib.attrsets.zipAttrsWith-example">
1459
-
<title>Summing a list of attribute sets of numbers</title>
1460
-
<programlisting><![CDATA[
1461
-
lib.attrsets.zipAttrsWith
1462
-
(name: vals: "${name} ${toString (builtins.foldl' (a: b: a + b) 0 vals)}")
1464
-
{ a = 1; b = 1; c = 1; }
1469
-
=> { a = "a 11"; b = "b 101"; c = "c 1001"; }
1470
-
]]></programlisting>
1474
-
<section xml:id="function-library-lib.attrsets.zipAttrs">
1475
-
<title><function>lib.attrsets.zipAttrs</function></title>
1477
-
<subtitle><literal>zipAttrs :: [ AttrSet ] -> AttrSet</literal>
1480
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.zipAttrs" />
1483
-
Merge sets of attributes and combine each attribute value in to a list. Similar to <xref linkend="function-library-lib.attrsets.zipAttrsWith" /> where the merge function returns a list of all values.
1489
-
<varname>sets</varname>
1493
-
A list of attribute sets to zip together.
1499
-
<example xml:id="function-library-lib.attrsets.zipAttrs-example">
1500
-
<title>Combining a list of attribute sets</title>
1501
-
<programlisting><![CDATA[
1502
-
lib.attrsets.zipAttrs
1504
-
{ a = 1; b = 1; c = 1; }
1509
-
=> { a = [ 1 10 ]; b = [ 1 100 ]; c = [ 1 1000 ]; }
1510
-
]]></programlisting>
1514
-
<section xml:id="function-library-lib.attrsets.recursiveUpdateUntil">
1515
-
<title><function>lib.attrsets.recursiveUpdateUntil</function></title>
1517
-
<subtitle><literal>recursiveUpdateUntil :: ( [ String ] -> AttrSet -> AttrSet -> Bool ) -> AttrSet -> AttrSet -> AttrSet</literal>
1520
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.recursiveUpdateUntil" />
1523
-
Does the same as the update operator <literal>//</literal> except that attributes are merged until the given predicate is verified. The predicate should accept 3 arguments which are the path to reach the attribute, a part of the first attribute set and a part of the second attribute set. When the predicate is verified, the value of the first attribute set is replaced by the value of the second attribute set.
1529
-
<varname>pred</varname>
1533
-
<literal>[ String ] -> AttrSet -> AttrSet -> Bool</literal>
1538
-
<varname>path</varname>
1542
-
The path to the values in the left and right hand sides.
1548
-
<varname>l</varname>
1552
-
The left hand side value.
1558
-
<varname>r</varname>
1562
-
The right hand side value.
1571
-
<varname>lhs</varname>
1575
-
The left hand attribute set of the merge.
1581
-
<varname>rhs</varname>
1585
-
The right hand attribute set of the merge.
1591
-
<example xml:id="function-library-lib.attrsets.recursiveUpdateUntil-example">
1592
-
<title>Recursively merging two attribute sets</title>
1593
-
<programlisting><![CDATA[
1594
-
lib.attrsets.recursiveUpdateUntil (path: l: r: path == ["foo"])
1596
-
# first attribute set
1602
-
#second attribute set
1608
-
foo.bar = 1; # 'foo.*' from the second set
1610
-
bar = 3; # 'bar' from the first set
1611
-
baz = 4; # 'baz' from the second set
1613
-
]]></programlisting>
1617
-
<section xml:id="function-library-lib.attrsets.recursiveUpdate">
1618
-
<title><function>lib.attrsets.recursiveUpdate</function></title>
1620
-
<subtitle><literal>recursiveUpdate :: AttrSet -> AttrSet -> AttrSet</literal>
1623
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.recursiveUpdate" />
1626
-
A recursive variant of the update operator <literal>//</literal>. The recursion stops when one of the attribute values is not an attribute set, in which case the right hand side value takes precedence over the left hand side value.
1632
-
<varname>lhs</varname>
1636
-
The left hand attribute set of the merge.
1642
-
<varname>rhs</varname>
1646
-
The right hand attribute set of the merge.
1652
-
<example xml:id="function-library-lib.attrsets.recursiveUpdate-example">
1653
-
<title>Recursively merging two attribute sets</title>
1654
-
<programlisting><![CDATA[
1657
-
boot.loader.grub.enable = true;
1658
-
boot.loader.grub.device = "/dev/hda";
1661
-
boot.loader.grub.device = "";
1664
-
boot.loader.grub.enable = true;
1665
-
boot.loader.grub.device = "";
1667
-
]]></programlisting>
1671
-
<section xml:id="function-library-lib.attrsets.recurseIntoAttrs">
1672
-
<title><function>lib.attrsets.recurseIntoAttrs</function></title>
1674
-
<subtitle><literal>recurseIntoAttrs :: AttrSet -> AttrSet</literal>
1677
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.recurseIntoAttrs" />
1680
-
Make various Nix tools consider the contents of the resulting attribute set when looking for what to build, find, etc.
1684
-
This function only affects a single attribute set; it does not apply itself recursively for nested attribute sets.
1690
-
<varname>attrs</varname>
1694
-
An attribute set to scan for derivations.
1700
-
<example xml:id="function-library-lib.attrsets.recurseIntoAttrs-example">
1701
-
<title>Making Nix look inside an attribute set</title>
1702
-
<programlisting><![CDATA[
1703
-
{ pkgs ? import <nixpkgs> {} }:
1705
-
myTools = pkgs.lib.recurseIntoAttrs {
1706
-
inherit (pkgs) hello figlet;
1709
-
]]></programlisting>
1713
-
<section xml:id="function-library-lib.attrsets.cartesianProductOfSets">
1714
-
<title><function>lib.attrsets.cartesianProductOfSets</function></title>
1716
-
<subtitle><literal>cartesianProductOfSets :: AttrSet -> [ AttrSet ]</literal>
1719
-
<xi:include href="./locations.xml" xpointer="lib.attrsets.cartesianProductOfSets" />
1722
-
Return the cartesian product of attribute set value combinations.
1728
-
<varname>set</varname>
1732
-
An attribute set with attributes that carry lists of values.
1738
-
<example xml:id="function-library-lib.attrsets.cartesianProductOfSets-example">
1739
-
<title>Creating the cartesian product of a list of attribute values</title>
1740
-
<programlisting><![CDATA[
1741
-
cartesianProductOfSets { a = [ 1 2 ]; b = [ 10 20 ]; }
1743
-
{ a = 1; b = 10; }
1744
-
{ a = 1; b = 20; }
1745
-
{ a = 2; b = 10; }
1746
-
{ a = 2; b = 20; }
1748
-
]]></programlisting>
pyrox.dev