freezable-trait

Available via cargo:

cargo add freezable-trait

Provides a wrapper around serde that eliminates a lot of the boilerplate I usually have to write.

#[derive(Debug, PartialEq)]
#[freezable] // <- here it is!
struct Example {
    pub field1: String,
    pub field2: i8,
    pub field3: bool,
    pub field4: f32,
}

impl Default for Example {
    fn default() -> Self {
        Self {
            _unknown_fields: HashMap::default(),
            field1: "def_test".to_string(),
            field2: 7,
            field3: true,
            field4: 12.5,
        }
    }
}

Freezable is an attribute marker (you just stick '#[freezable] on top of any struct to get it') which makes that struct a serde object with special per-field default initialization. It also provides some helper functions.

It requires the struct implement Default, as one of the things it does is apply serde's default fields to each individual field. In other words, if you deserialize a struct missing some fields but with others present, serde's default 'default' implementation is to provide you a completely clean default struct. Freezable structs will instead have any fields present in the partial deserialization present, with only missing fields initialized to the default values.

Freezable provides the following helper functions as trait members:

write_to_file(&self, path: PathBuf)
// Serializes the struct and writes it to a new file at the given Path.

write_to_file_str(&self, path: String)
// Serializes the struct and writes it to a new file at the given path string.
// Supports '~' and other relative positioning os-specifics via the shellexpand crate.

from_file(&self, path: PathBuf)
// Deserializes the struct from the file at the given path. If no file exists,
// you get Config::default(). If some fields are missing, present ones are initialized
// from the file and missing ones are initialized based on default values.

from_file_str(&self, path: &str)
// Does the above, but using a shellexpanded str path instead as described in write_to_file_str.

freeze_to_string(&self) -> String
// Returns the struct as a json string.

unfreeze_from_string(from: String)
// Deserializes the type from a given json string.