nu_cmd_lang/core_commands/
const_.rs

1use nu_engine::command_prelude::*;
2use nu_protocol::engine::CommandType;
3
4#[derive(Clone)]
5pub struct Const;
6
7impl Command for Const {
8    fn name(&self) -> &str {
9        "const"
10    }
11
12    fn description(&self) -> &str {
13        "Create a parse-time constant."
14    }
15
16    fn signature(&self) -> nu_protocol::Signature {
17        Signature::build("const")
18            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
19            .allow_variants_without_examples(true)
20            .required("const_name", SyntaxShape::VarWithOptType, "Constant name.")
21            .required(
22                "initial_value",
23                SyntaxShape::Keyword(b"=".to_vec(), Box::new(SyntaxShape::MathExpression)),
24                "Equals sign followed by constant value.",
25            )
26            .category(Category::Core)
27    }
28
29    fn extra_description(&self) -> &str {
30        r#"This command is a parser keyword. For details, check:
31  https://www.nushell.sh/book/thinking_in_nu.html"#
32    }
33
34    fn command_type(&self) -> CommandType {
35        CommandType::Keyword
36    }
37
38    fn search_terms(&self) -> Vec<&str> {
39        vec!["set", "let"]
40    }
41
42    fn run(
43        &self,
44        _engine_state: &EngineState,
45        _stack: &mut Stack,
46        _call: &Call,
47        _input: PipelineData,
48    ) -> Result<PipelineData, ShellError> {
49        // This is compiled specially by the IR compiler. The code here is never used when
50        // running in IR mode.
51        eprintln!(
52            "Tried to execute 'run' for the 'const' command: this code path should never be reached in IR mode"
53        );
54        unreachable!()
55    }
56
57    fn run_const(
58        &self,
59        _working_set: &StateWorkingSet,
60        _call: &Call,
61        _input: PipelineData,
62    ) -> Result<PipelineData, ShellError> {
63        Ok(PipelineData::empty())
64    }
65
66    fn is_const(&self) -> bool {
67        true
68    }
69
70    fn examples(&self) -> Vec<Example<'_>> {
71        vec![
72            Example {
73                description: "Create a new parse-time constant.",
74                example: "const x = 10",
75                result: None,
76            },
77            Example {
78                description: "Create a composite constant value",
79                example: "const x = { a: 10, b: 20 }",
80                result: None,
81            },
82        ]
83    }
84}
85
86#[cfg(test)]
87mod test {
88    use nu_protocol::engine::CommandType;
89
90    use super::*;
91
92    #[test]
93    fn test_examples() {
94        use crate::test_examples;
95
96        test_examples(Const {})
97    }
98
99    #[test]
100    fn test_command_type() {
101        assert!(matches!(Const.command_type(), CommandType::Keyword));
102    }
103}
nu_cmd_lang/core_commands/const_.rs

nu_cmd_lang/core_commands/
const_.rs
