Is it Possible to Add One Item of a List at a Time?

[ShiromMakkad]

Can I do something like:

struct MyStruct {
   num: i32
   properties: HashMap<&'static str, String>
}

MyStruct::builder().num(5).property("test", "test2").build(); 
MyStruct::builder().num(5).property("test", "test2").property("test2", "test3").build(); 
MyStruct::builder().num(5).build(); // Builds empty hashmap

I don't really need bon to handle properties -> property but the general idea of adding individual values and having access to into would be really nice. This behavior is in the AWS SDK for Rust and I want to match it.

I haven't read the entirety of the docs, but I didn't see anything in the overview or table of contents about this.

[Veetaha]

Hi, for this to work, you'll need to use #[builder(field)] (guide, reference) and define your custom "adder" methods like this:

use std::collections::HashMap;

#[derive(bon::Builder)]
struct MyStruct {
    #[builder(field)]
    properties: HashMap<&'static str, String>,

    num: i32,
}

impl<S: my_struct_builder::State> MyStructBuilder<S> {
    fn property(mut self, key: &'static str, value: impl Into<String>) -> Self {
        self.properties.insert(key, value.into());
        self
    }
}

fn main() {
    MyStruct::builder().num(5).property("test", "test2").build();
    MyStruct::builder()
        .num(5)
        .property("test", "test2")
        .property("test2", "test3")
        .build();
    MyStruct::builder().num(5).build(); // Builds empty hashmap
}

Alternatively, consider bon::map! {}, which provides a *Map type literal and converts keys/values with Into::into() automatically. Plus it does some simple key uniqueness checks at compile time.

[ShiromMakkad]

Awesome thanks!