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Document null dynamic attrs

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Shea Levy 2014-03-10 07:09:07 -04:00 committed by Eelco Dolstra
parent 049a379ec6
commit 2f2a20ed18
2 changed files with 15 additions and 1 deletions
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5
doc/manual/release-notes.xml
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@ -25,7 +25,10 @@
attribute names (e.g. <literal>set."${foo}"</literal>). In the attribute names (e.g. <literal>set."${foo}"</literal>). In the
case where the attribute name is just a single antiquotation, case where the attribute name is just a single antiquotation,
the quotes can be dropped (e.g. the above example can be written the quotes can be dropped (e.g. the above example can be written
<literal>set.${foo}</literal>).</para></listitem> <literal>set.${foo}</literal>). If an attribute name inside of a
set declaration evaluates to <literal>"${null}"</literal> (e.g.
<literal>{ ${null} = false; }</literal>), then that attribute is not added
added to the set.</para></listitem>
</itemizedlist> </itemizedlist>

11
doc/manual/writing-nix-expressions.xml
View file

@ -871,6 +871,17 @@ This will evaluate to <literal>123</literal> if
coerced to a string and <literal>456</literal> otherwise (again coerced to a string and <literal>456</literal> otherwise (again
assuming <literal>bar</literal> is antiquotable).</para> assuming <literal>bar</literal> is antiquotable).</para>
<para>In the special case where an attribute name inside of a set declaration
evaluates to <literal>"${null}"</literal> (which is normally an error, as
<literal>null</literal> is not antiquotable), that attribute is simply not
added to the set:
<programlisting>
{ ${if foo then "bar" else null} = true; }</programlisting>
This will evaluate to <literal>{}</literal> if <literal>foo</literal>
evaluates to <literal>false</literal>.</para>
</simplesect> </simplesect>