# 2.7 Rusty\_v8

## Overview 

V8 and Deno have different core programming languages: V8 uses C++, while Deno uses Rust. To bridge this gap, the innovative "rusty\_v8" library was developed. This library creates efficient Rust bindings to V8's complex C++ APIs, achieving seamless integration without additional call overhead. By doing so, rusty\_v8 enables the harmonious interaction between V8's C++ foundation and Deno's Rust infrastructure. 

When working with APIs, rusty\_v8 harmonizes with V8's APIs through a straightforward translation of functionalities, maintaining efficiency without extra burdens. This synchronization is a testament to the library's ability to foster compatibility and efficiency. The creation of rusty\_v8 demonstrates the successful integration of languages and technologies, showcasing the potential for dynamic interaction between different programming languages. This connection highlights the compatibility of C++ and Rust, emphasizing the commitment to efficiency and seamless integration within the Deno ecosystem.

## Example

Let's examine a few code examples to better understand how rusty\_v8 works. Analyzing its practical uses will help us comprehend rusty\_v8 more effectively. A specific aspect to investigate is the way rusty\_v8 implements Strings.

```
pub fn length(&self) -> usize {
    unsafe { v8__String__Length(self) as usize }
}
```

The String class in Rust includes a function that calculates the length of a string. When this "length" function is called, it activates the "v8\_\_String\_\_Length" code, which is written in C++. This code determines the length of the v8 string data type. There is a direct and simple relationship between the function and the code, with a one-to-one correspondence. This means that the function and code are closely linked, providing a clear connection between the Rust String class and v8's string data type.

```
int v8__String__Length(const v8::String& self) { 
    return self.Length(); } 
}
```

Let's explore another example within the rusty\_v8 module, specifically the 'parse' function:

```
pub fn parse<'s>(
  scope: &mut HandleScope<'s>,
  json_string: Local<'_, String>,
) -> Option<Local<'s, Value>> {
  unsafe {
    scope
      .cast_local(|sd| v8__JSON__Parse(sd.get_current_context(), &*json_string))
  }
}
```

Rusty\_v8 has a parse function that matches the v8\_\_JSON\_\_Parse function. The parse function, written in C++, acts as a connector to access the corresponding function in the v8 library. This connection enables Rusty\_v8 to utilize v8's capabilities for parsing JSON data.

```
const v8::Value* v8__JSON__Parse(const v8::Context& context,
                                 const v8::String& json_string) {
  return maybe_local_to_ptr(
      v8::JSON::Parse(ptr_to_local(&context), ptr_to_local(&json_string)));
}
```

Rusty\_v8 generally matches the v8 API in most cases. For more information on rusty\_v8, visit their GitHub page at <https://github.com/denoland/rusty_v8>. Now, let's discuss Tokio, a tool that enables Deno to perform tasks asynchronously. This means Deno can handle tasks efficiently without getting stuck on one task, improving its overall performance and responsiveness.


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