# MultiversX WASM AssemblyScript (Proof of concept)

A proof of concept to make MultiversX smart contracts in AssemblyScript.

## ⚠️ Warning ⚠️

THIS IS ONLY EXPERIMENTAL, DO NOT USE IT IN PRODUCTION !

The aim of this repo is to make a proof of concept and ONLY a proof of concept. The code is neither clean nor safe nor optimized !

## Getting started

### AssemblyScript

AssemblyScript is nearly the same as Typescript, but there is still some difference, please check <https://www.assemblyscript.org/> to have more informations.

### Contract development

#### Build the empty contract

If you only want to try writing smart contracts with this framework do the following steps :

* Clone the following repo : <https://github.com/gfusee/mx-sdk-as-empty.git>
* In order to compile the contract you should run the command `npm run build`

And you're done ! The contract is compiled into the `build` folder.

Feel free to check examples contracts inside the `contracts/examples` folder, these are reproduction of `mx-sdk-rs` examples contracts.

#### Test the contract via mandos

If you installed mxpy via mxpy-up you only need to run `npm run test` in the root folder to execute scenarios.

If you have a custom installation of erdpy, here are the steps to execute mandos scenarios :

* Compile the contract (steps above)
* Find your `run-scenarios` executable path inside your mxpy installation
* Inside the root folder of the project, run the `<path to run-scenarios> mandos` command

## Documentation

There is currently no documentation, feel free to check examples inside the `contract/examples` folder.

If after that you have any question, feel free to DM me !

## What's not (properly) working

### Structs/classes & enums

Structs and enums are workings but with some limitations.

In order to create a classes which is compatible with the framework you should annotate it with either `@struct` or `@enumType` :

```
@struct
export class Human {
    name: ElrondString
    age: ElrondU64
    wallet: ManagedAddress
}
```

or

```
@enumType
export enum Animal {
    Cat,
    Dog,
    Spider
}
```

You should be aware of the four following limitations :

* Constructor should have no parameter. It is planned in the future to allow constructors with params, for now, you can use statics methods as a workaround.
* They should have only managed properties types (those exported from this framework)
* Enums are converted into classes at compilation. So `switch` statements may not work as expected, please use `if` instead.
* They are allocated on the heap. More explanations below.

### Statics and generics

There is a limitation related to Typescript, we cannot define static methods on interfaces so we cannot call them on generic parameters.

A good workaround is to instantiate dummy objects to have access to those methods. This may lead to useless VM calls, I'm hunting these useless calls to remove them.

### Closures

AssemblyScript has a SEVERE limitation about closures. Inside a closure we cannot use a variable declared outside, for example this code works :

```
myBiguints.forEach(biguint => {
    if (biguint == BigUint.zero()) {
        throw new Error("BigUint should be greater than 0 !")
    }
})
```

But the following code does not work :

```
const sum = BigUint.zero()
myBiguints.forEach(biguint => {
    sum += biguint //does NOT compile because sum is declared outside the closure
})
```

This issue is known by the AssemblyScript and should be fixed in the future : <https://github.com/AssemblyScript/assemblyscript/issues/798>

### Heap allocations

The biggest limitation of AssemblyScript I'm facing is that classes does not act as C structs, they are always allocated on the heap and this lead to big issues. I used a heavy workaround for some classes (ManagedBuffer, BigUint, ...) but not for all classes because this take a lot of time to refactor all.

This issue is known by the AssemblyScript team : <https://github.com/AssemblyScript/assemblyscript/issues/2254>


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