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| author | Vincent Ambo <tazjin@tvl.su> | 2023-10-10T10·54+0300 |
|---|---|---|
| committer | clbot <clbot@tvl.fyi> | 2023-10-10T11·18+0000 |
| commit | da648b4707fb1d8fd6a9679669d2eb36a5f0832c (patch) | |
| tree | 26f88d0399bfc5e62e7d80c5b9f79c35686fe145 /nix | |
| parent | 0ad059ddfed1482713b1f3a73eedfcbb4a23a692 (diff) | |
docs(nix-1p): add section about the merge operator r/6765
Without the examples, some behaviour of the merge operator might not be clear from the previous description. Due to how pervasively the operator is used, I think it warrants a separate section. This fixes https://github.com/tazjin/nix-1p/issues/16 Change-Id: Iecba5f1cb749bef0a4987b3fc5642832a92c18d5 Reviewed-on: https://cl.tvl.fyi/c/depot/+/9599 Autosubmit: tazjin <tazjin@tvl.su> Tested-by: BuildkiteCI Reviewed-by: flokli <flokli@flokli.de>
Diffstat (limited to 'nix')
| -rw-r--r-- | nix/nix-1p/README.md | 34 |
1 files changed, 32 insertions, 2 deletions
diff --git a/nix/nix-1p/README.md b/nix/nix-1p/README.md index 72297a5551..5d2dce83bf 100644 --- a/nix/nix-1p/README.md +++ b/nix/nix-1p/README.md @@ -19,6 +19,7 @@ and entering code snippets there. - [Language constructs](#language-constructs) - [Primitives / literals](#primitives--literals) - [Operators](#operators) + - [`//` (merge) operator](#-merge-operator) - [Variable bindings](#variable-bindings) - [Functions](#functions) - [Multiple arguments (currying)](#multiple-arguments-currying) @@ -113,8 +114,6 @@ rec { a = 15; b = a * 2; } Nix has several operators, most of which are unsurprising: -Make sure to understand the `//`-operator, as it is used quite a lot and is -probably the least familiar one. | Syntax | Description | |---------------------------|-----------------------------------------------------------------------------| | `+`, `-`, `*`, `/` | Numerical operations | @@ -131,6 +130,37 @@ probably the least familiar one. | `left // right` | Merge `left` & `right` attribute sets, with the right set taking precedence | +### `//` (merge) operator + +The `//`-operator is used pervasively in Nix code. You should familiarise +yourself with it, as it is likely also the least familiar one. + +It merges the left and right attribute sets given to it: + +```nix +{ a = 1; } // { b = 2; } + +# yields { a = 1; b = 2; } +``` + +Values from the right side take precedence: + +```nix +{ a = "left"; } // { a = "right"; } + +# yields { a = "right"; } +``` + +The merge operator does *not* recursively merge attribute sets; + +```nix +{ a = { b = 1; }; } // { a = { c = 2; }; } + +# yields { a = { c = 2; }; } +``` + +Helper functions for recursive merging exist in the [`lib` library](#pkgslib). + ## Variable bindings Bindings in Nix are introduced locally via `let` expressions, which make some |