HashMap storing values as multiple types

help
1

Dear Rustaceans,
I have a HashMap called apple, it stores values of different types with a enum called Var. I want to compare the values of the HashMap with an if statement, for example apple["isRed?"] == true, to achieve this, I wanted a method to return the value of the enum, for example Var::Bool, but I cannot get it to work, I tried with a match statement but the compiler expects T but gets &bool, for example Self::Bool(out) => out,.
Hard to explain, here is the playground:

Thank you in advance,
FatGoose

2

See this answer for an outline of your get_value method:

1 Like
3

Note that this is a trigger-happy footgun. Any mistake made in the type and you'll get None when you expected Some(&T).

It's better to use the matches macro:

if matches!(apple.get("Name"), Some(Var::String(x)) if x == "Pink Lady")
4

Is there a reason your apple isn't a normal struct? It seems like it would be more naturally expressed as a struct.

5

Thank you, that helped.

Solution 
fn main()
{
    let mut apple = std::collections::HashMap::from([
        ("Name", Var::String("Pink Lady".to_string())),
        ("Amount", Var::Int(12)),
        ("Red", Var::Bool(true)),
        ("Size in cm", Var::Float(3.4)),
        ("Sellable?", Var::Bool(false)),
    ]);

    if apple["Name"].get_value::<String>().unwrap() == "Pink Lady"
        && *apple["Red"].get_value().unwrap()
        && *apple["Size in cm"].get_value::<f64>().unwrap() >= 1.2
    {
        *apple.entry("Sellable?").or_insert(Var::Bool(true)) = Var::Bool(true);
        println!("The apple is sellable. {}", *apple["Sellable?"].get_value::<bool>().unwrap());
    }
}

enum Var
{
    Bool(bool),
    Int(i32),
    Float(f64),
    String(String),
}
impl Var
{
    fn get_value<T: 'static>(&self) -> Option<&T>
    {
        let output: &dyn std::any::Any = match self 
        {
            Self::Bool(value) => value,
            Self::Int(value) => value,
            Self::Float(value) => value,
            Self::String(value) => value,
        };
        if output.downcast_ref::<T>().is_none()
        {
            panic!("Option<T> should not be 'None'");
        }
        output.downcast_ref()
    }
}

EDIT: fixed mistakes in code.

6

Hello erelde,
there is the reason, because I will later on implement function, that allows a user to add attributes to the apple.