Implement GetHashCode for ArrayStackItem, MapStackItem, StructStackItem, InteropInterface about neo-vm

[dicarlo2]

Also would need to implement it for the enumerator/iterator wrappers in neo core.

[dicarlo2]

Alternatively, just move the implementation of GetHashCode to the primitive types.

[dicarlo2]

I would also recommend making sure Equals is implemented for all things that can be InteropInterface, e.g. all of the state classes

[erikzhang]

Is there a specific scenario that you need this for?

In JavaScript, an array is serialized as a string as a key.

var a = [1, 2];
var o = {};
o[a] = 100;
alert(o["1,2"]);

So I don't see why it is necessary to implement these.

[dicarlo2]

JavaScript also has a Map class that we've implemented in neo-one which is supposed to function the same as the C# equivalent assuming no custom hash code or equals implementation - that is, references may be used as keys. E.g.

const a = new Map();
const b = [1, 2];
a.set(b, 'hello');
console.log(a.get([1, 2])) // -> undefined
console.log(a.get(b)) // -> 'hello'

[erikzhang]

I think it is still impossible to implement a JavaScript Map.

console.log(a.get([1, 2])) // -> undefined

This line returns an undefined, but in NeoVM it throws an exception.

neo-vm/src/neo-vm/ExecutionEngine.cs

Lines 748 to 752 in 1874219

	if (!map.TryGetValue(key, out item))
	{
	State |= VMState.FAULT;
	return;
	}

[dicarlo2]

@erikzhang we check if the map has the key before calling pickitem so that we have a chance to return undefined. This is blocking NEO-ONE TypeScript smart contracts, can we revisit implementing this?