Add `into_` counterparts for all `as_` methods

[matthew-piziak]

Background

Conversion method naming conventions

RFC 7087 and The Rust Style Guidelines define the following naming conventions for conversion methods:

Prefix	Cost	Consumes convertee
as_	Free	No
to_	Expensive	No
into_	Variable	Yes

Proposed Enhancement

Currently yaml-rust provides as_ methods (as_str, as_hash, as_vec, etc.) on the impl Yaml. These methods obey the listed convention and do not consume the Yaml object. Adding into_ methods that consume the Yaml object would allow some callers to reduce their overall memory footprint.

Use Case

Code Review Answer (last paragraph)

[matthew-piziak]

I plan to submit a pull request for this ticket in the next few days.

[matthew-piziak]

Here's what I currently have:

Macro and Methods

macro_rules! define_as (
    ($name:ident, $t:ident, $yt:ident) => (
pub fn $name(&self) -> Option<$t> {
    match *self {
        Yaml::$yt(v) => Some(v),
        _ => None
    }
}
    );
);

macro_rules! define_as_ref (
    ($name:ident, $t:ty, $yt:ident) => (
pub fn $name(&self) -> Option<$t> {
    match *self {
        Yaml::$yt(ref v) => Some(v),
        _ => None
    }
}
    );
);

macro_rules! define_into (
    ($name:ident, $t:ty, $yt:ident) => (
pub fn $name(self) -> Option<$t> {
    match self {
        Yaml::$yt(v) => Some(v),
        _ => None
    }
}
    );
); 

impl Yaml {
    define_as!(as_bool, bool, Boolean);
    define_as!(as_i64, i64, Integer);

    define_as_ref!(as_str, &str, String);
    define_as_ref!(as_hash, &Hash, Hash);
    define_as_ref!(as_vec, &Array, Array);

    define_into!(into_bool, bool, Boolean);
    define_into!(into_i64, i64, Integer); 
    define_into!(into_string, String, String);
    define_into!(into_hash, Hash, Hash);
    define_into!(into_vec, Array, Array);

    pub fn is_null(&self) -> bool {
        match *self {
            Yaml::Null => true,
            _ => false
        }
    }

    pub fn is_badvalue(&self) -> bool {
        match *self {
            Yaml::BadValue => true,
            _ => false
        }
    }

    pub fn as_f64(&self) -> Option<f64> {
        match *self {
            Yaml::Real(ref v) => {
                v.parse::<f64>().ok()
            },
            _ => None
        }
    }

    pub fn into_f64(self) -> Option<f64> {
        match self {
            Yaml::Real(v) => {
                v.parse::<f64>().ok()
            },
            _ => None
        }
    }
}

Naïve test case

I'd like to avoid clone but I'm new to Rust and I don't know what the correct improvement is. I would iterate over Yaml to consume the elements directly but although Yaml supports indexing, it does not implement IntoIterator. Is implementing IntoIterator a reasonable choice?

    #[test]
    fn test_plain_datatype_with_into_methods() {
        let s =
"
- 'string'
- \"string\"
- string
- 123
- -321
- 1.23
- -1e4
- true
- false
- !!str 0
- !!int 100
- !!float 2
- !!bool true
- !!bool false
- 0xFF 
- 0o77
- [ 0xF, 0xF ]
- +12345
- [ true, false ]
";
        let out = YamlLoader::load_from_str(&s).unwrap();
        let doc = &out[0]; 

        assert_eq!(doc[0].clone().into_string().unwrap(), "string");
        assert_eq!(doc[1].clone().into_string().unwrap(), "string");
        assert_eq!(doc[2].clone().into_string().unwrap(), "string");
        assert_eq!(doc[3].clone().into_i64().unwrap(), 123);
        assert_eq!(doc[4].clone().into_i64().unwrap(), -321);
        assert_eq!(doc[5].clone().into_f64().unwrap(), 1.23);
        assert_eq!(doc[6].clone().into_f64().unwrap(), -1e4);
        assert_eq!(doc[7].clone().into_bool().unwrap(), true);
        assert_eq!(doc[8].clone().into_bool().unwrap(), false);
        assert_eq!(doc[9].clone().into_string().unwrap(), "0");
        assert_eq!(doc[10].clone().into_i64().unwrap(), 100);
        assert_eq!(doc[11].clone().into_f64().unwrap(), 2.0);
        assert_eq!(doc[12].clone().into_bool().unwrap(), true);
        assert_eq!(doc[13].clone().into_bool().unwrap(), false);
        assert_eq!(doc[14].clone().into_i64().unwrap(), 255);
        assert_eq!(doc[15].clone().into_i64().unwrap(), 63);
        assert_eq!(doc[16][0].clone().into_i64().unwrap(), 15);
        assert_eq!(doc[16][1].clone().into_i64().unwrap(), 15);
        assert_eq!(doc[17].clone().into_i64().unwrap(), 12345);
        assert!(doc[18][0].clone().into_bool().unwrap());
        assert!(!doc[18][1].clone().into_bool().unwrap());
    }

[matthew-piziak]

I've implemented IntoIterator and removed the calls to clone.