Nix Language Quirks: Difference between revisions
imported>Danbst added old let syntax |
imported>Danbst added function argument destructuring |
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Note, that it isn't equivalent to <code>with rec { x = 1; y = x + 1; body = y; }; body</code> because of mentioned <code>with</code> and <code>let</code> quirk, but is same as <code>rec { x = 1; y = x + 1; body = y; }.body</code> | Note, that it isn't equivalent to <code>with rec { x = 1; y = x + 1; body = y; }; body</code> because of mentioned <code>with</code> and <code>let</code> quirk, but is same as <code>rec { x = 1; y = x + 1; body = y; }.body</code> | ||
== Something that looks like both record attribute and <code>let</code>-binding == | |||
Destructuring function argument - is a great feature of Nix. | |||
<nowiki> | |||
nix-repl> f = { x ? 1, y ? 2 }: x + y | |||
nix-repl> f { } | |||
3</nowiki> | |||
The fact that we can add <code>@args</code> argument assignment is also cool | |||
<nowiki> | |||
nix-repl> f = { x ? 1, y ? 2, ... }@args: with args; x + y + z | |||
nix-repl> f { z = 3; } | |||
6</nowiki> | |||
But don't be fooled, <code>args</code> doesn't necessarily contain <code>x</code> and <code>y</code>: | |||
<nowiki> | |||
nix-repl> f = { x ? 1, y ? 2, ... }@args: args.x + args.y + args.z | |||
nix-repl> f { z = 3;} | |||
error: attribute ‘x’ missing, at (string):1:30</nowiki> | |||
These <code>x</code> and <code>y</code> are in fact <code>let</code>-bindings, but overridable ones. | |||