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Diffstat (limited to 'doc/manual/src/language/values.md')
-rw-r--r-- | doc/manual/src/language/values.md | 26 |
1 files changed, 21 insertions, 5 deletions
diff --git a/doc/manual/src/language/values.md b/doc/manual/src/language/values.md index c85124278..2ae3e143a 100644 --- a/doc/manual/src/language/values.md +++ b/doc/manual/src/language/values.md @@ -164,9 +164,17 @@ Note that lists are only lazy in values, and they are strict in length. An attribute set is a collection of name-value-pairs (called *attributes*) enclosed in curly brackets (`{ }`). +An attribute name can be an identifier or a [string](#string). +An identifier must start with a letter (`a-z`, `A-Z`) or underscore (`_`), and can otherwise contain letters (`a-z`, `A-Z`), numbers (`0-9`), underscores (`_`), apostrophes (`'`), or dashes (`-`). + +> *name* = *identifier* | *string* \ +> *identifier* ~ `[a-zA-Z_][a-zA-Z0-9_'-]*` + Names and values are separated by an equal sign (`=`). Each value is an arbitrary expression terminated by a semicolon (`;`). +> *attrset* = `{` [ *name* `=` *expr* `;` `]`... `}` + Attributes can appear in any order. An attribute name may only occur once. @@ -182,21 +190,29 @@ Example: This defines a set with attributes named `x`, `text`, `y`. -Attributes can be selected from a set using the `.` operator. For -instance, +Attributes can be accessed with the [`.` operator](./operators.md#attribute-selection). + +Example: ```nix { a = "Foo"; b = "Bar"; }.a ``` -evaluates to `"Foo"`. It is possible to provide a default value in an -attribute selection using the `or` keyword. For example, +This evaluates to `"Foo"`. + +It is possible to provide a default value in an attribute selection using the `or` keyword. + +Example: ```nix { a = "Foo"; b = "Bar"; }.c or "Xyzzy" ``` -will evaluate to `"Xyzzy"` because there is no `c` attribute in the set. +```nix +{ a = "Foo"; b = "Bar"; }.c.d.e.f.g or "Xyzzy" +``` + +will both evaluate to `"Xyzzy"` because there is no `c` attribute in the set. You can use arbitrary double-quoted strings as attribute names: |