nushell/crates/nu-command/src/dataframe/expressions/alias.rs

use super::super::values::NuExpression;

use nu_engine::CallExt;
use nu_protocol::{
    ast::Call,
    engine::{Command, EngineState, Stack},
    Category, Example, PipelineData, ShellError, Signature, SyntaxShape,
};

#[derive(Clone)]
pub struct ExprAlias;

impl Command for ExprAlias {
    fn name(&self) -> &str {
        "dfr as"
    }

    fn usage(&self) -> &str {
        "Creates an alias expression"
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .required(
                "Alias name",
                SyntaxShape::String,
                "Alias name for the expression",
            )
            .category(Category::Custom("expressions".into()))
    }

    fn examples(&self) -> Vec<Example> {
        vec![Example {
            description: "Creates and alias expression",
            example: "(dfr col a | df as new_a)",
            result: None,
        }]
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let alias: String = call.req(engine_state, stack, 0)?;

        let expr = NuExpression::try_from_pipeline(input, call.head)?;
        let expr: NuExpression = expr.into_polars().alias(alias.as_str()).into();

        Ok(PipelineData::Value(
            NuExpression::into_value(expr, call.head),
            None,
        ))
    }
}