#dynamic #float #conversion #dynamically-typed


Support for dynamically-typed values in run-time

17 breaking releases

0.18.0 Jul 23, 2023
0.16.0 Apr 15, 2023
0.10.0 Mar 31, 2023

#209 in Algorithms

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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
  • Nanosecond grade timestamp
  • Any dynamically-typed object wrapped in envelope
  • Complex numbers for i64 and f64
  • Maps
  • Associations
  • None
  • Error
  • Metrics as a Vector of TIMESTAMP->F64 samples

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.

Function name Description
Value::from_float() Create dynamic object from f64 float number
Value::from_float32() Create dynamic object from f32 float number
Value::from_integer() Create dynamic object from i64 float number
Value::from_integer32() Create dynamic object from i32 float number
Value::from_bool() Create dynamic object from boolean value
Value::from_string() Create dynamic object from Rust String
Value::from_str() Create dynamic object from Rust &str
Value::from_bin() Create dynamic object of type BINARY from Vec
Value::pair() Create dynamic object of type PAIR from the pair of values
Value::list() Create empty dynamic object of type LIST
Value::from_list() Create dynamic object of type LIST and initialize it from Vec
Value::from_dict() Create dynamic object of type MAP and initialize it from HashMap<String, Value>
Value::dict() Create dynamic empty object of type MAP
Value::none() Create dynamic object that wraps value of None
Value::nodata() Create dynamic object that contains no data
Value::now() Return dynamic object of type TIME containing current number of nanosecods from UNIX_EPOCH
Value::exit() Return dynamic object of type EXIT
Value::metrics() Return dynamic object of type METRICS for 128 samples
Value::metrics_n(n) Return dynamic object of type METRICS for n samples
Value::lambda() Return dynamic object of type LAMBDA
Value::to_lambda() Return dynamic object of type LAMBDA created from Vector
Value::result() Return dynamic object of type RESULT
Value::to_result() Return dynamic object of type RESULT created from Vector
Value::from_metrics() Return dynamic object created from Vec of Metrics
Value::from_complex_int() Return dynamic object created from Complex
Value::from_complex_float() Return dynamic object created from Complex
Value::conv() Converting of the object of one type to another

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.

Function name Description
Value::cast_float() Return f64 number from FLOAT object
Value::cast_integer() Return i64 number from INTEGER object
Value::cast_bool() Return boolean from BOOL object
Value::cast_string() Return String from STRING object
Value::cast_bin() Return Vec from BINARY object
Value::cast_list() Return Vec from LIST/PAIR object
Value::cast_result() Return Vec from RESULT object
Value::cast_lambda() Return Vec from LAMBDA object
Value::cast_pair() Return Vec from PAIR object
Value::cast_pair_x() Return Value from PAIR X object
Value::cast_pair_y() Return Value from PAIR Y object
Value::cast_metrics() Return Vec from METRICS object
Value::cast_fifo() Return next Value from FIFO object
Value::cast_queue() Return next Value from QUEUE object
Value::cast_dict() Return HashMap<String,Value> from MAP,INFO,CONFIG,ASSOCIATION objects
Value::cast_complex_int() Return Complex from CINTEGER object
Value::cast_complex_float() Return Complex from CFLOAT object
Value::export_float() Return Vec from Value object


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 set attributes to the Value

Value attributes is a Vector of the values that stored in the Value object. You can assign any number of the Value objects stored as attributes of the Value object. Attributes are serailize-able and wrap-able.

Function name Description
Value.attr(Vec) Set vector of values as an attributes of the Value object
Value.attr_add(Value) Add a Value to the end of attributes list of the Value object. Returns duplicate of Value object
Value.attr_merge(Vec) Merge Vector of Values and current attributes of the Value object. Returns duplicate of Value object
Value.attr_len() Return number of attributes of the Value object


// Create object
let v = Value::from(42 as i64).unwrap()
                // Set the attributes of the object
                .attr(vec![Value::from(41.0 as f64).unwrap()])
                // And merge some extra attributes. The first attribute now have a value of 42.0
                .attr_merge(vec![Value::from(42.0 as f64).unwrap()]);

How to serialize and deserialize dynamically-typed values

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

Function name Description
Value::to_json() Return JSON representation of dynamically-typed value
Value::to_binary() Return Bincode representation of dynamically-typed value
Value::from_json() Takes string containing JSON representation of the dynamically-typed object and return re-created Value object
Value::from_binary() Takes Vec containing Bincode representation of the dynamically-typed object and return re-created Value object
Value.wrap() Return a ENVELOPE object containing a Bincode representation of object
Value.unwrap() If object is ENVELOPE unpack binary representation of enclosed object, recreate it and return


// 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();

Integration of dynamically-typed values with serde_json crate.

Crate rust_dynamic is capable to export Value object to serde_json::value::Value

Function name Description
Value.as_json_value() Function converts Value object to serde_json::value::Value


// This call will create a Value object of type PAIR and on-the-fly exports it
// to the serde_json::value::Value object that can be processed as any other Value object created by serde_json crate.
let v = Value::pair(Value::from_int(1), Value::from_int(2)).as_json_value();

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.

Function name Description
Value.bind() Takes a reference to a function that accepts Value as a parameter, that function is called with passed current object and new Value object returned
Value::bind_values() Takes a reference to a function that accepts two Values as a parameter, and two values. New Value object returned that is result of programmatic binding of the values
Value.fmap() Execute function to each element of the LIST or to the value and return new Value
Value.map_float() Execute function to each FLOAT element of the LIST or to the value and return new Value
Value.push() Ether add a new value to the list, or return a new Value
Value.maybe() Takes a function which is if returns true, Value.maybe() returns value, if false Value::none()
Value::left_right() Takes a function which is if returns true, and a references on two Values. Value::left_right() returns clone of first value, if function return true, second othewise
Value::freduce() Takes two parameters - function which takes two values and returning a single value and initial value, reducing dynamic value to a single value by applying function to all elements

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;
// 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()

Example of reducing

// First, we shall create a list of the values
let mut v = Value::from_list(
    vec![Value::from_float(41.0 as f64),
    Value::from_float(1.0 as f64)]);
// Then reduce this list applying function that sums "accumulator" and current value
v = v.freduce(
    |x: Value,y: Value| -> Value { x+y },
    Value::from_float(0.0 as f64));
// This function shall return a single FLOAT value wrapping number 42.0

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());


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