What in the Value ?

Rust's core strength is its ability to provide memory safety and performance guarantees at compile-time, which is achieved through its ownership and borrowing system. But ability for the developer to handle a dynamic data types defined at run-time for the applications written in Rust is still important endeavor and it is improving versatility of the application while providing an ability to handle a wide range of use cases.

Various interpreted DSL languages created in Rust uses run-time dynamic data type system created for the specific language. Excellent crate Serde also implements trait Value that's allow to handle dynamic datatypes in run-time. But none of those solutions is not perfect for a Rust developers as they ether focus on specific DSL or handling JSON values.

rust_dynamic is a crate, created for Rust language, implementing primitives that will be helping to Rust developer with the specific issue of handling dynamic data types defined at run-time. Currently, rust_dynamic supports following data types:

• Integer, internally represented as i64
• Float, internally represented as f64
• Boolean
• String, internally represented as String
• Pair, as a pair of dynamic values
• List, as a list of dynamic values
• Binary, as a Vector of u8 values

Dynamic values are wrapped and stored inside a Value structure and could be cast-able back into original Rust value.

use rust_dynamic::value::Value;

let mut value = Value::from(42).unwrap();
println!("Type of the stored value is {}", &value.type_name());
println!("Dynamic value of the value is {:?}", &value.cast_integer());

What are the properties of dynamically-typed objects

• Value objects can wrap value of any supported type and they are functionally pure. Once you assigned the value, you can not change it, with one exception. Any attempts of change will result in generation of a new Value object. But you can push a new value to the object of List type, without re-creating a new object.
• All dynamically-typed objects are hash-able, so you can use them as the keys in HasMap objects.
• All dynamically-typed objects holds full information about stored data type.
• All dynamically-typed objects stores a unique object identifier.
• All dynamically-typed objects serialize-able to both JSON and a Bincode.
• You can iterate over All dynamically-typed objects.
• You can create attributes attached to wrapped data.
• Basic math operation Add/Sub/Mul/Div supported for FLOAT and INTEGER types.
• String concatenation and multiplication supported.

How to create a dynamically-typed values

rust_dynamic crate supports a number of function-primitives that will take a raw value and return a wrapped Dynamic object.

There are generic function Value::from() that will automatically cast proper data type and ether return object or error message.

How to cast Rust value from dynamically-typed values

rust_dynamic supports a number of casting functions that will try to extract wrapped value from the object that holds dynamically-typed value.

Example:

use rust_dynamic::value::Value;

// First we create a dynamically-typed value from a raw static value
let mut value = Value::from(42).unwrap();

// Then we can cast raw value back from the dynamic object
let raw_value = value.cast_integer().unwrap()

How to serialize and deserialize dynamically-typed values

There are two serialization formats that rust_dynamic presently supports: JSON and Bincode.

Example:

// This call will create a new dynamic value
let mut data = Value::from(42 as i64).unwrap();
// This call will serialize object to Bincode format
let bin_out = data.to_binary().unwrap();
// This will re-create an object from it's Bincode representation
let mut data2 = Value::from_binary(bin_out).unwrap();

Functional operations with dynamically-typed values

While rust_dynamic crate is not strive to provide a full-featured functional interface to the dynamic values, some functionality that specific to a Functional programming has been implemented.

Example of mapping:

// First, we define a function which will cast value of f64 and apply f64.sin() operation
fn comp_sin(value: Value) -> Value {
    match value.data {
        Val::F64(f_val) => {
            return Value::from_float(f64::sin(f_val));
        }
        _ => return value,
    }
}
// Then we create a single value object (map could be epplied to ether list or single value object)
let mut v = Value::from(42.0).unwrap();
// Now v contains result of computation
v = v.map_value(comp_sin);

Example of binding

// First, let's create a "binding function" which will takes two Value objects and return a new Value
// In our example, simple sum() will be performed
fn sum_of_values(v1: Value, v2: Value) -> Value {
    v1 + v2
}
// Then let's create two values
let v1 = Value::from(41.0 as f64).unwrap();
let v2 = Value::from(1.0 as f64).unwrap();
// Value referred as _s_ now contains value of 42.0
let s = Value::bind_values(sum_of_values, v1, v2);

Example of maybe()

// First, we create a function that will check if v is float and is 42
fn if_value_is_42(v: &Value) -> bool {
    if v.cast_float().unwrap() == 42.0 {
        return true;
    }
    false
}
// And because it is, v is object of Value(42.0)
// Otherwise it would be Value::none()
let v = Value::from(42.0 as f64).unwrap()
        .maybe(if_value_is_42);

How to use dynamically-typed objects as HashMap keys

use std::collections::HashMap;

// This call will create a key object. Key object can be of any supported type
let key = Value::from(42.0 as f64).unwrap();

// Then we are creating a HashMap
let mut h: HashMap<Value, String> = HashMap::new();

// and store a key->value association
h.insert(key, "value".to_string());

How to iterate over dynamically-typed objects

let mut c = 0.0;
// Let's create a object of LIST type and push two elements into list
let v = Value::list()
        .push(Value::from(1.0 as f64).unwrap())
        .push(Value::from(41.0 as f64).unwrap());
// We can iterate over dynamically-typed object
for i in v {
    c += i.cast_float().unwrap();
}

How to map over dynamically-typed objects

In this example we are applying f64::sin function to all iterable values of the dynamically-typed object

let mut v = Value::from(42.0).unwrap();
v = v.map_float(f64::sin);

How to use a math operations with dynamically-typed objects

At this moment, only FLOAT and INTEGER objects supported math operations.

// Let's create x and y objects both of FLOAT type
let mut x = Value::from(1.0 as f64).unwrap();
let y = Value::from(41.0 as f64).unwrap();
// And perform math operation as usual
x = x + y;

How to concatenate string objects

At this moment, only STRING object supports that operation.

// Let's create x and y objects both of STRING type
let mut x = Value::from("Hello").unwrap();
// Then perform operation as usual, x shall be a object of STRING type containing string "Hello world"
let y = Value::from(" world").unwrap();
x = x + y;

How to convert from String to Float

// This call returns the object of type FLOAT
let val = Value::from("42").unwrap().conv(FLOAT).unwrap();

Functional features of rust_dynamic

Create and use of Applicative

You can create an Applicative that is wrapping a function and apply a Value object with wrapped value to Applicative. For example:

// First, as usual, we are defining function, that will be wrapped in Applicative
fn comp_sin(value: Value) -> Value {
    match value.data {
        Val::F64(f_val) => {
            return Value::from_float(f64::sin(f_val));
        }
        _ => return value,
    }
}

// Create applicative and wrap a function
let sin = Applicative::new(comp_sin);
// Then apply a Value to a wrapped function
let res = sin.apply(Value::from(42.0).unwrap());