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Guida alla migrazione di AssemblyScript

Up until now, Subgraphs have been using one of the first versions of AssemblyScript⁠ (v0.6). Finally we’ve added support for the newest one available⁠ (v0.19.10)! 🎉

That will enable Subgraph developers to use newer features of the AS language and standard library.

This guide is applicable for anyone using graph-cli/graph-ts below version 0.22.0. If you’re already at a higher than (or equal) version to that, you’ve already been using version 0.19.10 of AssemblyScript 🙂

Note: As of 0.24.0, graph-node can support both versions, depending on the apiVersion specified in the Subgraph manifest.

Caratteristiche

Nuova funzionalità

  • TypedArrays can now be built from ArrayBuffers by using the new wrap static method⁠ (v0.8.1⁠)
  • New standard library functions: String#toUpperCase, String#toLowerCase, String#localeCompareand TypedArray#set (v0.9.0⁠)
  • Added support for x instanceof GenericClass (v0.9.2⁠)
  • Added StaticArray<T>, a more efficient array variant (v0.9.3⁠)
  • Added Array<T>#flat (v0.10.0⁠)
  • Implemented radix argument on Number#toString (v0.10.1⁠)
  • Added support for separators in floating point literals (v0.13.7⁠)
  • Added support for first class functions (v0.14.0⁠)
  • Add builtins: i32/i64/f32/f64.add/sub/mul (v0.14.13⁠)
  • Implement Array/TypedArray/String#at (v0.18.2⁠)
  • Added support for template literal strings (v0.18.17⁠)
  • Add encodeURI(Component) and decodeURI(Component) (v0.18.27⁠)
  • Add toString, toDateString and toTimeString to Date (v0.18.29⁠)
  • Add toUTCString for Date (v0.18.30⁠)
  • Add nonnull/NonNullable builtin type (v0.19.2⁠)

Ottimizzazioni

  • Math functions such as exp, exp2, log, log2 and pow have been replaced by faster variants (v0.9.0⁠)
  • Slightly optimize Math.mod (v0.17.1⁠)
  • Cache more field accesses in std Map and Set (v0.17.8⁠)
  • Optimize for powers of two in ipow32/64 (v0.18.2⁠)

Altro

  • The type of an array literal can now be inferred from its contents (v0.9.0⁠)
  • Updated stdlib to Unicode 13.0.0 (v0.10.0⁠)

Come aggiornare?

  1. Change your mappings apiVersion in subgraph.yaml to 0.0.9:
...dataSources:  ...    mapping:      ...      apiVersion: 0.0.9      ...
  1. Update the graph-cli you’re using to the latest version by running:
# se è installato globalmentenpm install --global @graphprotocol/graph-cli@latest# o nel proprio subgraph, se è una dipendenza di devnpm install --save-dev @graphprotocol/graph-cli@latest
  1. Do the same for graph-ts, but instead of installing globally, save it in your main dependencies:
npm install --save @graphprotocol/graph-ts@latest
  1. Seguire il resto della guida per correggere le modifiche alla lingua.
  2. Run codegen and deploy again.

Cambiamenti di rottura

Nullabilità

Nella versione precedente di AssemblyScript, era possibile creare codice come questo:

function load(): Value | null { ... }let maybeValue = load();maybeValue.aMethod();

Tuttavia, nella versione più recente, poiché il valore è nullable, è necessario effettuare un controllo, come questo:

let maybeValue = load()if (maybeValue) {  maybeValue.aMethod() // `maybeValue` is not null anymore}

Oppure forzarla in questo modo:

let maybeValue = load()! // breaks in runtime if value is nullmaybeValue.aMethod()

If you are unsure which to choose, we recommend always using the safe version. If the value doesn’t exist you might want to just do an early if statement with a return in you Subgraph handler.

Shadowing della variabile

Before you could do variable shadowing⁠ and code like this would work:

let a = 10let b = 20let a = a + b

Tuttavia ora questo non è più possibile e il compilatore restituisce questo errore:

ERROR TS2451: Cannot redeclare block-scoped variable 'a' let a = a + b; ~~~~~~~~~~~~~in assembly/index.ts(4,3)

È necessario rinominare le variabili duplicate se si dispone di un’ombreggiatura delle variabili.

Confronti nulli

By doing the upgrade on your Subgraph, sometimes you might get errors like these:

ERROR TS2322: Type '~lib/@graphprotocol/graph-ts/common/numbers/BigInt | null' is not assignable to type '~lib/@graphprotocol/graph-ts/common/numbers/BigInt'.     if (decimals == null) {                     ~~~~ in src/mappings/file.ts(41,21)

To solve you can simply change the if statement to something like this:

if (!decimals) {  // or  if (decimals === null) {

Lo stesso vale se si fa != invece di ==.

Casting

The common way to do casting before was to just use the as keyword, like this:

let byteArray = new ByteArray(10)let uint8Array = byteArray as Uint8Array // equivalent to: <Uint8Array>byteArray

Tuttavia, questo funziona solo in due scenari:

  • Primitive casting (between types such as u8, i32, bool; eg: let b: isize = 10; b as usize);
  • Upcasting sull’ereditarietà delle classi (subclasse → superclasse)

Esempi:

// primitive castinglet a: usize = 10let b: isize = 5let c: usize = a + (b as usize)
// upcasting on class inheritanceclass Bytes extends Uint8Array {}let bytes = new Bytes(2)// <Uint8Array>bytes // same as: bytes as Uint8Array

There are two scenarios where you may want to cast, but using as/<T>var isn’t safe:

  • Downcasting sull’ereditarietà delle classi (superclasse → subclasse)
  • Tra due tipi che condividono una superclasse
// downcasting on class inheritanceclass Bytes extends Uint8Array {}let uint8Array = new Uint8Array(2)// <Bytes>uint8Array // breaks in runtime :(
// between two types that share a superclassclass Bytes extends Uint8Array {}class ByteArray extends Uint8Array {}let bytes = new Bytes(2)// <ByteArray>bytes // breaks in runtime :(

For those cases, you can use the changetype<T> function:

// downcasting on class inheritanceclass Bytes extends Uint8Array {}let uint8Array = new Uint8Array(2)changetype<Bytes>(uint8Array) // works :)
// between two types that share a superclassclass Bytes extends Uint8Array {}class ByteArray extends Uint8Array {}let bytes = new Bytes(2)changetype<ByteArray>(bytes) // works :)

If you just want to remove nullability, you can keep using the as operator (or <T>variable), but make sure you know that value can’t be null, otherwise it will break.

// rimuovere la nullitàlet previousBalance = AccountBalance.load(balanceId) // AccountBalance | nullif (previousBalance != null) {  return previousBalance as AccountBalance // safe remove null}let newBalance = new AccountBalance(balanceId)

For the nullability case we recommend taking a look at the nullability check feature⁠, it will make your code cleaner 🙂

Inoltre abbiamo aggiunto alcuni metodi statici in alcuni tipi per facilitare il casting, che sono:

  • Bytes.fromByteArray
  • Bytes.fromUint8Array
  • BigInt.fromByteArray
  • ByteArray.fromBigInt

Verifica della nullità con accesso alle proprietà

To use the nullability check feature⁠ you can use either if statements or the ternary operator (? and :) like this:

let something: string | null = 'data'let somethingOrElse = something ? something : 'else'// orlet somethingOrElseif (something) {  somethingOrElse = something} else {  somethingOrElse = 'else'}

However that only works when you’re doing the if / ternary on a variable, not on a property access, like this:

class Container {  data: string | null}let container = new Container()container.data = 'data'let somethingOrElse: string = container.data ? container.data : 'else' // non viene compilato

Che produce questo errore:

ERROR TS2322: Type '~lib/string/String | null' is not assignable to type '~lib/string/String'.   let somethingOrElse: string = container.data ? container.data : "else";                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Per risolvere questo problema, si può creare una variabile per l’accesso alla proprietà, in modo che il compilatore possa fare la magia del controllo di annullabilità:

class Container {  data: string | null}let container = new Container()container.data = 'data'let data = container.datalet somethingOrElse: string = data ? data : 'else' // viene compilato benissimo :)

Sovraccarico dell’operatore con accesso alle proprietà

Se si tenta di sommare (ad esempio) un tipo nullable (da un accesso a una proprietà) con uno non nullable, il compilatore di AssemblyScript, invece di dare un avviso di errore in fase di compilazione sul fatto che uno dei valori è nullable, si limita a compilare in silenzio, dando la possibilità che il codice si interrompa in fase di esecuzione.

class BigInt extends Uint8Array {  @operator('+')  plus(other: BigInt): BigInt {    // ...  }}class Wrapper {  public constructor(public n: BigInt | null) {}}let x = BigInt.fromI32(2)let y: BigInt | null = nullx + y // give compile time error about nullabilitylet wrapper = new Wrapper(y)wrapper.n = wrapper.n + x // non dà errori in fase di compilazione come dovrebbe

We’ve opened a issue on the AssemblyScript compiler for this, but for now if you do these kind of operations in your Subgraph mappings, you should change them to do a null check before it.

let wrapper = new Wrapper(y)if (!wrapper.n) {  wrapper.n = BigInt.fromI32(0)}wrapper.n = wrapper.n + x // ora `n` è garantito essere un BigInt

Inizializzazione del valore

Se si dispone di codice come questo:

var value: Type // nullvalue.x = 10value.y = 'content'

It will compile but break at runtime, that happens because the value hasn’t been initialized, so make sure your Subgraph has initialized their values, like this:

var value = new Type() // initializedvalue.x = 10value.y = 'content'

Inoltre, se si hanno proprietà nullable in un’entità GraphQL, come questa:

type Total @entity {  id: Bytes!  amount: BigInt}

E avete un codice simile a questo:

let total = Total.load('latest')if (total === null) {  total = new Total('latest')}total.amount = total.amount + BigInt.fromI32(1)

You’ll need to make sure to initialize the total.amount value, because if you try to access like in the last line for the sum, it will crash. So you either initialize it first:

let total = Total.load('latest')if (total === null) {  total = new Total('latest')  total.amount = BigInt.fromI32(0)}total.tokens = total.tokens + BigInt.fromI32(1)

Or you can just change your GraphQL schema to not use a nullable type for this property, then we’ll initialize it as zero on the codegen step 😉

type Total @entity {  id: Bytes!  amount: BigInt!}
let total = Total.load('latest')if (total === null) {  total = new Total('latest') // inizializza già le proprietà non nulle}total.amount = total.amount + BigInt.fromI32(1)

Inizializzazione delle proprietà della classe

Se si esportano classi con proprietà che sono altre classi (dichiarate dall’utente o dalla libreria standard) come questa:

class Thing {}export class Something {  value: Thing}

The compiler will error because you either need to add an initializer for the properties that are classes, or add the ! operator:

export class Something {  constructor(public value: Thing) {}}// orexport class Something {  value: Thing  constructor(value: Thing) {    this.value = value  }}// orexport class Something {  value!: Thing}

Inizializzazione del Array

The Array class still accepts a number to initialize the length of the list, however you should take care because operations like .push will actually increase the size instead of adding to the beginning, for example:

let arr = new Array<string>(5) // ["", "", "", "", ""]arr.push('something') // ["", "", "", "", "", "something"] // size 6 :(

A seconda dei tipi utilizzati, ad esempio quelli nullable, e del modo in cui vi si accede, si potrebbe verificare un errore di runtime come questo:

ERRO Handler skipped due to execution failure, error: Mapping aborted at ~lib/array.ts, line 110, column 40, with message: Element type must be nullable if array is holey  wasm backtrace:     0: 0x19c4 - <unknown>!~lib/@graphprotocol/graph-ts/index/format         1: 0x1e75 - <unknown>!~lib/@graphprotocol/graph-ts/common/collections/Entity#constructor        2: 0x30b9 - <unknown>!node_modules/@graphprotocol/graph-ts/global/global/id_of_type

To actually push at the beginning you should either, initialize the Array with size zero, like this:

let arr = new Array<string>(0) // []arr.push('something') // ["something"]

Oppure si dovrebbe mutare tramite indice:

let arr = new Array<string>(5) // ["", "", "", "", ""]arr[0] = 'something' // ["something", "", "", "", ""]

Schema GraphQL

This is not a direct AssemblyScript change, but you may have to update your schema.graphql file.

Ora non è più possibile definire campi nei tipi che sono elenchi non nulli. Se si ha uno schema come questo:

type Something @entity {  id: Bytes!}type MyEntity @entity {  id: Bytes!  invalidField: [Something]! # no longer valid}

You’ll have to add an ! to the member of the List type, like this:

type Something @entity {  id: Bytes!}type MyEntity @entity {  id: Bytes!  invalidField: [Something!]! # valid}

This changed because of nullability differences between AssemblyScript versions, and it’s related to the src/generated/schema.ts file (default path, you might have changed this).

Altro

  • Aligned Map#set and Set#add with the spec, returning this (v0.9.2⁠)
  • Arrays no longer inherit from ArrayBufferView, but are now distinct (v0.10.0⁠)
  • Classes initialized from object literals can no longer define a constructor (v0.10.0⁠)
  • The result of a ** binary operation is now the common denominator integer if both operands are integers. Previously, the result was a float as if calling Math/f.pow (v0.11.0⁠)
  • Coerce NaN to false when casting to bool (v0.14.9⁠)
  • When shifting a small integer value of type i8/u8 or i16/u16, only the 3 respectively 4 least significant bits of the RHS value affect the result, analogous to the result of an i32.shl only being affected by the 5 least significant bits of the RHS value. Example: someI8 << 8 previously produced the value 0, but now produces someI8 due to masking the RHS as 8 & 7 = 0 (3 bits) (v0.17.0⁠)
  • Bug fix of relational string comparisons when sizes differ (v0.17.8⁠)