Nitwel
Nitwel•9mo ago

rusty_v8, how to mutate scope outside anonymous function

Hi, I'm trying to use the v8 rust create to run javascript on my backend and now I'm stuck at how to modify a Vec<String> declared outside a anonymous function scope, as said function gets used to be the callback of a v8::Function. 
let logs = Vec::new();

let log_callback = |scope: &mut v8::HandleScope,
                    args: v8::FunctionCallbackArguments,
                    mut rv: v8::ReturnValue| {
    let arg = args.get(0);
    let arg_string = arg.to_string(scope).unwrap().to_rust_string_lossy(scope);

    logs.push(arg_string); // <---- How can I do this?

    rv.set(v8::undefined(scope).into());
};

// https://github.com/matejkoncal/v8-experiments/blob/master/src/main.rs
let log_fn = v8::Function::new(scope, log_callback).unwrap().into();
let name = v8::String::new(scope, "log").unwrap().into();
let global = context.global(scope);
global.set(scope, name, log_fn);
let logs = Vec::new();

let log_callback = |scope: &mut v8::HandleScope,
                    args: v8::FunctionCallbackArguments,
                    mut rv: v8::ReturnValue| {
    let arg = args.get(0);
    let arg_string = arg.to_string(scope).unwrap().to_rust_string_lossy(scope);

    logs.push(arg_string); // <---- How can I do this?

    rv.set(v8::undefined(scope).into());
};

// https://github.com/matejkoncal/v8-experiments/blob/master/src/main.rs
let log_fn = v8::Function::new(scope, log_callback).unwrap().into();
let name = v8::String::new(scope, "log").unwrap().into();
let global = context.global(scope);
global.set(scope, name, log_fn);
The errors I'm getting are the following: 
error[E0277]: the trait bound `{closure@src\post_run_js.rs:23:24: 25:49}: MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>` is not satisfied
    --> src\post_run_js.rs:35:43
     |
35   |     let log_fn = v8::Function::new(scope, log_callback).unwrap().into();
     |                  -----------------        ^^^^^^^^^^^^ the trait `for<'a, 's, 'b> Fn(&'a mut HandleScope<'s>, FunctionCallbackArguments<'s>, ReturnValue<'b>)` is not implemented for closure `{closure@src\post_run_js.rs:23:24: 25:49}`, which is required by `{closure@src\post_run_js.rs:23:24: 25:49}: MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>`
     |                  |
     |                  required by a bound introduced by this call
     |
     = note: required for `extern "C" fn(*const FunctionCallbackInfo)` to implement `v8::support::MapFnFrom<{closure@src\post_run_js.rs:23:24: 25:49}>`
     = note: required for `{closure@src\post_run_js.rs:23:24: 25:49}` to implement `MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>`
note: required by a bound in `v8::function::<impl Function>::new`
    --> C:\Users\NilsPC\.cargo\registry\src\index.crates.io-6f17d22bba15001f\v8-0.105.1\src\function.rs:1006:20
     |
1004 |   pub fn new<'s>(
     |          --- required by a bound in this associated function
1005 |     scope: &mut HandleScope<'s>,
1006 |     callback: impl MapFnTo<FunctionCallback>,
     |                    ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `v8::function::<impl Function>::new`

error[E0277]: the trait bound `&mut Vec<std::string::String>: Copy` is not satisfied in `{closure@src\post_run_js.rs:23:24: 25:49}`
    --> src\post_run_js.rs:35:43
     |
23   |       let log_callback = |scope: &mut v8::HandleScope,
     |  ________________________-
24   | |                         args: v8::FunctionCallbackArguments,
25   | |                         mut rv: v8::ReturnValue| {
     | |________________________________________________- within this `{closure@src\post_run_js.rs:23:24: 25:49}`
...
35   |       let log_fn = v8::Function::new(scope, log_callback).unwrap().into();
     |                    -----------------        ^^^^^^^^^^^^ within `{closure@src\post_run_js.rs:23:24: 25:49}`, the trait `Copy` is not implemented for `&mut Vec<std::string::String>`, which is required by `{closure@src\post_run_js.rs:23:24: 25:49}: MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>`
     |                    |
     |                    required by a bound introduced by this call
     |
     = note: `Copy` is implemented for `&Vec<std::string::String>`, but not for `&mut Vec<std::string::String>`
error[E0277]: the trait bound `{closure@src\post_run_js.rs:23:24: 25:49}: MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>` is not satisfied
    --> src\post_run_js.rs:35:43
     |
35   |     let log_fn = v8::Function::new(scope, log_callback).unwrap().into();
     |                  -----------------        ^^^^^^^^^^^^ the trait `for<'a, 's, 'b> Fn(&'a mut HandleScope<'s>, FunctionCallbackArguments<'s>, ReturnValue<'b>)` is not implemented for closure `{closure@src\post_run_js.rs:23:24: 25:49}`, which is required by `{closure@src\post_run_js.rs:23:24: 25:49}: MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>`
     |                  |
     |                  required by a bound introduced by this call
     |
     = note: required for `extern "C" fn(*const FunctionCallbackInfo)` to implement `v8::support::MapFnFrom<{closure@src\post_run_js.rs:23:24: 25:49}>`
     = note: required for `{closure@src\post_run_js.rs:23:24: 25:49}` to implement `MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>`
note: required by a bound in `v8::function::<impl Function>::new`
    --> C:\Users\NilsPC\.cargo\registry\src\index.crates.io-6f17d22bba15001f\v8-0.105.1\src\function.rs:1006:20
     |
1004 |   pub fn new<'s>(
     |          --- required by a bound in this associated function
1005 |     scope: &mut HandleScope<'s>,
1006 |     callback: impl MapFnTo<FunctionCallback>,
     |                    ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `v8::function::<impl Function>::new`

error[E0277]: the trait bound `&mut Vec<std::string::String>: Copy` is not satisfied in `{closure@src\post_run_js.rs:23:24: 25:49}`
    --> src\post_run_js.rs:35:43
     |
23   |       let log_callback = |scope: &mut v8::HandleScope,
     |  ________________________-
24   | |                         args: v8::FunctionCallbackArguments,
25   | |                         mut rv: v8::ReturnValue| {
     | |________________________________________________- within this `{closure@src\post_run_js.rs:23:24: 25:49}`
...
35   |       let log_fn = v8::Function::new(scope, log_callback).unwrap().into();
     |                    -----------------        ^^^^^^^^^^^^ within `{closure@src\post_run_js.rs:23:24: 25:49}`, the trait `Copy` is not implemented for `&mut Vec<std::string::String>`, which is required by `{closure@src\post_run_js.rs:23:24: 25:49}: MapFnTo<extern "C" fn(*const FunctionCallbackInfo)>`
     |                    |
     |                    required by a bound introduced by this call
     |
     = note: `Copy` is implemented for `&Vec<std::string::String>`, but not for `&mut Vec<std::string::String>`
Please be aware that I'm still very new to Rust so extra insights into what's going wrong here would be very helpful!
2 Replies
fazbdillah
fazbdillah•2mo ago
For the logs vector, you need to wrap it in Rc and RefCell: https://stackoverflow.com/questions/52994205/what-is-the-standard-way-to-call-a-mutable-method-in-a-rc-wrapped-object As for the v8 thing, I've not try it myself.
Stack Overflow
What is the standard way to call a mutable method in a Rc-wrapped o...
In the following code, I am trying to change the value of a refcounted object by calling one of its methods: use std::rc::Rc; fn main() { let mut x = Rc::new(Thing { num: 50 }); x.
fazbdillah
fazbdillah•2mo ago
For the function error, you actually can't use closure because the type impl MapFnTo<FunctionCallback> doesn't allow to. Closure is when you use external var inside the |arg| {} form. See this playground.

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