Nix Language Quirks: Difference between revisions

Line 75:

== Imports and namespaces ==

~~There is~~ a keyword <code>import</code>, but it's equivalent in other languages is <code>eval</code>. It ~~can~~ be used for namespacing ~~too~~:

Nix includes a keyword <code>import</code>, but it's equivalent in other languages is <code>eval</code>.

It is typically be used for namespacing:

<syntaxHighlight lang=nix>let

Line 83:

Line 85:

pkgs.runCommand (lib.strings.removePrefix ".... </syntaxHighlight>

consider ~~using~~ <code>import</code> here as using <code>qualified import ...</code> in Haskell or <code>import ...</code> in Python.

consider the use of <code>import</code> here similar to using <code>qualified import ...</code> in Haskell or <code>import ...</code> in Python. Another (discouraged and increasingly uncommon) way of importing is [https://nix.dev/manual/nix/2.24/language/syntax#with-expressions <code>with import ...;</code>], which corresponds to Python <code>from ... import *</code>. This use of <code>with</code> imports everything from the target into scope, which has numerous potential gotchas and problems, and so instead using [https://nix.dev/guides/best-practices#with-scopes <code>inherit</code>] is encouraged and preferred.

Another way of importing is <code>with import ...;</code>, which corresponds to Python <code>from ... import *</code>.

~~But because~~ of ~~not very great IDE support in Nix,~~ <code>with ~~import ...;</code> is discouraged. Rather use <code>inherit~~</code>, ~~especially if you are targeting source code for Nix newcomers:~~

~~<syntaxHighlight lang=nix>~~

~~let~~

~~lib = import <nixpkgs/lib>;~~

~~inherit (lib.strings)~~

~~removePrefix removeSuffix~~

;

~~inherit (lib.lists)~~

~~isList init drop~~

;

in

~~removePrefix ... </syntaxHighlight>~~

~~<code>inherit</code>~~ has ~~higher priority than <code>with</code>~~, and ~~conflicts with <code>let<~~/~~code>~~

~~<syntaxHighlight lang=~~nix>

~~nix-repl> let pkgs = { x = 1; }; x = 2; x = 3; inherit (pkgs) x; in x~~

~~error: attribute ‘x’ at (string):1:31 already defined at (string):1:24 <~~/~~syntaxHighlight>~~

~~This makes it a sane citizen of Nix lanugage... except it has a twin, called <code>{ inherit ...; }<~~/~~code>. They DON'T do the same~~ - <code>~~let~~ inherit ~~...~~</code> ~~adds let-bindings,~~ and ~~<code>{ inherit ...; }</code> adds attributes to a record~~.

== builtins.replaceStrings key match on "" ==

@@ Line 75: / Line 75: @@
 == Imports and namespaces ==
-There is a keyword <code>import</code>, but it's equivalent in other languages is  <code>eval</code>. It can be used for namespacing too:
+Nix includes a keyword <code>import</code>, but it's equivalent in other languages is <code>eval</code>.
+It is typically be used for namespacing:
   <syntaxHighlight lang=nix>let
@@ Line 83: / Line 85: @@
    pkgs.runCommand (lib.strings.removePrefix ".... </syntaxHighlight>
-consider using <code>import</code> here as using <code>qualified import ...</code> in Haskell or <code>import ...</code> in Python.
+consider the use of <code>import</code> here similar to using <code>qualified import ...</code> in Haskell or <code>import ...</code> in Python. Another (discouraged and increasingly uncommon) way of importing is [https://nix.dev/manual/nix/2.24/language/syntax#with-expressions <code>with import ...;</code>], which corresponds to Python <code>from ... import *</code>. This use of <code>with</code> imports everything from the target into scope, which has numerous potential gotchas and problems, and so instead using [https://nix.dev/guides/best-practices#with-scopes <code>inherit</code>] is encouraged and preferred.
-Another way of importing is <code>with import ...;</code>, which corresponds to Python <code>from ... import *</code>.
-But because of not very great IDE support in Nix, <code>with import ...;</code> is discouraged. Rather use <code>inherit</code>, especially if you are targeting source code for Nix newcomers:
-  <syntaxHighlight lang=nix>
-let
-  lib = import <nixpkgs/lib>;
-  inherit (lib.strings)
-    removePrefix removeSuffix
-  ;
-  inherit (lib.lists)
-    isList init drop
-  ;
-in
-  removePrefix ... </syntaxHighlight>
-<code>inherit</code> has higher priority than <code>with</code>, and conflicts with <code>let</code>
-  <syntaxHighlight lang=nix>
-nix-repl> let pkgs = { x = 1; }; x = 2; x = 3; inherit (pkgs) x; in x
-error: attribute ‘x’ at (string):1:31 already defined at (string):1:24 </syntaxHighlight>
-This makes it a sane citizen of Nix lanugage... except it has a twin, called <code>{ inherit ...; }</code>. They DON'T do the same - <code>let inherit ...</code> adds let-bindings, and <code>{ inherit ...; }</code> adds attributes to a record.
 == builtins.replaceStrings key match on "" ==