mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-12-16 09:53:17 +00:00
121 lines
3.6 KiB
XML
121 lines
3.6 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
|
xml:id="chap-functions">
|
|
|
|
<title>Functions reference</title>
|
|
|
|
<para>
|
|
The nixpkgs repository has several utility functions to manipulate Nix expressions.
|
|
</para>
|
|
|
|
<section xml:id="sec-pkgs-overridePackages">
|
|
<title>pkgs.overridePackages</title>
|
|
|
|
<para>
|
|
This function inside the nixpkgs expression (<varname>pkgs</varname>)
|
|
can be used to override the set of packages itself.
|
|
</para>
|
|
<para>
|
|
Warning: this function is expensive and must not be used from within
|
|
the nixpkgs repository.
|
|
</para>
|
|
<para>
|
|
Example usage:
|
|
|
|
<programlisting>let
|
|
pkgs = import <nixpkgs> {};
|
|
newpkgs = pkgs.overridePackages (self: super: {
|
|
foo = super.foo.override { ... };
|
|
};
|
|
in ...</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
The resulting <varname>newpkgs</varname> will have the new <varname>foo</varname>
|
|
expression, and all other expressions depending on <varname>foo</varname> will also
|
|
use the new <varname>foo</varname> expression.
|
|
</para>
|
|
|
|
<para>
|
|
The behavior of this function is similar to <link
|
|
linkend="sec-modify-via-packageOverrides">config.packageOverrides</link>.
|
|
</para>
|
|
|
|
<para>
|
|
The <varname>self</varname> parameter refers to the final package set with the
|
|
applied overrides. Using this parameter may lead to infinite recursion if not
|
|
used consciously.
|
|
</para>
|
|
|
|
<para>
|
|
The <varname>super</varname> parameter refers to the old package set.
|
|
It's equivalent to <varname>pkgs</varname> in the above example.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section xml:id="sec-pkg-override">
|
|
<title><pkg>.override</title>
|
|
|
|
<para>
|
|
The function <varname>override</varname> is usually available for all the
|
|
derivations in the nixpkgs expression (<varname>pkgs</varname>).
|
|
</para>
|
|
<para>
|
|
It is used to override the arguments passed to a function.
|
|
</para>
|
|
<para>
|
|
Example usages:
|
|
|
|
<programlisting>pkgs.foo.override { arg1 = val1; arg2 = val2; ... }</programlisting>
|
|
<programlisting>pkgs.overridePackages (self: super: {
|
|
foo = super.foo.override { barSupport = true ; };
|
|
})</programlisting>
|
|
<programlisting>mypkg = pkgs.callPackage ./mypkg.nix {
|
|
mydep = pkgs.mydep.override { ... };
|
|
})</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
In the first example, <varname>pkgs.foo</varname> is the result of a function call
|
|
with some default arguments, usually a derivation.
|
|
Using <varname>pkgs.foo.override</varname> will call the same function with
|
|
the given new arguments.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section xml:id="sec-lib-makeOverridable">
|
|
<title>lib.makeOverridable</title>
|
|
|
|
<para>
|
|
The function <varname>lib.makeOverridable</varname> is used make the result
|
|
of a function easily customizable. This utility only makes sense for functions
|
|
that accept an argument set and return an attribute set.
|
|
</para>
|
|
|
|
<para>
|
|
Example usage:
|
|
|
|
<programlisting>f = { a, b }: { result = a+b; }
|
|
c = lib.makeOverridable f { a = 1; b = 2; }</programlisting>
|
|
|
|
</para>
|
|
|
|
<para>
|
|
The variable <varname>c</varname> is the value of the <varname>f</varname> function
|
|
applied with some default arguments. Hence the value of <varname>c.result</varname>
|
|
is <literal>3</literal>, in this example.
|
|
</para>
|
|
|
|
<para>
|
|
The variable <varname>c</varname> however also has some additional functions, like
|
|
<link linkend="sec-pkg-override">c.override</link> which can be used to
|
|
override the default arguments. In this example the value of
|
|
<varname>(c.override { a = 4; }).result</varname> is 6.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
</chapter>
|