Trait Env 

pub trait Env {
    type GetVariableError;
    type AssignVariableError;

    // Required methods
    fn get_variable(
        &self,
        name: &str,
    ) -> Result<Option<&str>, Self::GetVariableError>;
    fn assign_variable(
        &mut self,
        name: &str,
        value: String,
        location: Range<usize>,
    ) -> Result<(), Self::AssignVariableError>;
}

Interface for accessing variables during evaluation

This crate does not implement any mechanism for storing variables. The caller of eval must provide an implementation of this trait, which is used to access variables that appear in the evaluated expression.

Required Associated Types

type GetVariableError

Object returned on a variable access error

type AssignVariableError

Object returned on an assignment error

Required Methods

fn get_variable( &self, name: &str, ) -> Result<Option<&str>, Self::GetVariableError>

Returns the value of the specified variable.

This function must return:

• Ok(Some(v)) if the variable is defined and has the value v,
• Ok(None) if the variable is not defined, or
• Err(error) if an error occurs.

fn assign_variable( &mut self, name: &str, value: String, location: Range<usize>, ) -> Result<(), Self::AssignVariableError>

Assigns a new value to the specified variable.

The location parameter is the index range to the evaluated expression where the assignment appears.

Implementations on Foreign Types

impl Env for BTreeMap<String, String>

type GetVariableError = Infallible

type AssignVariableError = Infallible

fn get_variable(&self, name: &str) -> Result<Option<&str>, Infallible>

fn assign_variable( &mut self, name: &str, value: String, _location: Range<usize>, ) -> Result<(), Infallible>

impl Env for HashMap<String, String>

type GetVariableError = Infallible

type AssignVariableError = Infallible

fn get_variable(&self, name: &str) -> Result<Option<&str>, Infallible>

fn assign_variable( &mut self, name: &str, value: String, _location: Range<usize>, ) -> Result<(), Infallible>

Implementors