feat: List scalars (#36)

Author: disq

src/scalar/list.test.ts

@@ -0,0 +1,42 @@
+import test from 'ava';
+
+import { Int64 } from './int64.js';
+import { List } from './list.js';
+
+test('list', (t) => {
+  const l = new List(Int64);
+  t.deepEqual(l, new List(Int64));
+
+  l.value = [new Int64(17), new Int64(19), new Int64(null)];
+  t.is(l.length, 3);
+});
+
+test('list equality', (t) => {
+  const l1 = new List(Int64);
+  l1.value = [new Int64(17), new Int64(19), new Int64(null)];
+
+  const l2 = new List(Int64);
+  l2.value = [new Int64(17), new Int64(19), new Int64(null)];
+
+  t.deepEqual(l1, l2);
+});
+
+test('list inequality', (t) => {
+  const l1 = new List(Int64);
+  l1.value = new Int64(4);
+
+  const l2 = new List(Int64);
+  l2.value = new Int64(7);
+
+  t.notDeepEqual(l1, l2);
+});
+
+test('list equality when invalid', (t) => {
+  const l1 = new List(Int64);
+  l1.value = new Int64(null);
+
+  const l2 = new List(Int64);
+  l2.value = new Int64(null);
+
+  t.deepEqual(l1, l2);
+});

src/scalar/list.ts

@@ -0,0 +1,86 @@
+import { DataType, List as ArrowList } from '@apache-arrow/esnext-esm';
+
+import { Scalar } from './scalar.js';
+import { isInvalid, NULL_VALUE } from './util.js';
+
+type TVector<T extends Scalar<unknown>> = T[];
+
+export class List<T extends Scalar<unknown>> implements Scalar<TVector<T>> {
+  private _type: new (value?: unknown) => T;
+  private _valid = false;
+  private _value: TVector<T> = [];
+
+  constructor(scalarType: new (value?: unknown) => T, initialValue?: unknown) {
+    this._type = scalarType;
+    if (!isInvalid(initialValue)) this.value = initialValue;
+  }
+
+  get dataType(): DataType {
+    return new ArrowList(this._type.prototype.dataType);
+  }
+
+  set value(inputValue: unknown) {
+    if (isInvalid(inputValue)) {
+      this._valid = false;
+      this._value = [];
+      return;
+    }
+
+    const inputArray = Array.isArray(inputValue) ? inputValue : [inputValue];
+    const temporaryVector: TVector<T> = [];
+
+    if (inputArray.length > 0) {
+      const firstItemScalar = new this._type();
+      firstItemScalar.value = inputArray[0];
+      const firstItemType = Object.getPrototypeOf(firstItemScalar).constructor;
+
+      for (const item of inputArray) {
+        const scalar = new this._type();
+        scalar.value = item;
+
+        if (Object.getPrototypeOf(scalar).constructor !== firstItemType) {
+          throw new Error(
+            `Type mismatch: All items should be of the same type as the first item. Expected type ${
+              firstItemType.name
+            }, but got ${Object.getPrototypeOf(scalar).constructor.name}`,
+          );
+        }
+
+        temporaryVector.push(scalar);
+      }
+
+      this._value = temporaryVector;
+      this._valid = true; // List becomes valid if we successfully process values
+      return;
+    }
+
+    this._valid = true; // An empty list is valid
+  }
+
+  get valid(): boolean {
+    return this._valid;
+  }
+
+  get value(): TVector<T> {
+    return this._value;
+  }
+
+  toString(): string {
+    if (!this._valid) {
+      return NULL_VALUE;
+    }
+    return `[${this._value.map((v) => v.toString()).join(', ')}]`;
+  }
+
+  get length(): number {
+    return this._value.length;
+  }
+
+  // If you need an equality method, you can add an equals method similar to the Python __eq__
+  equals(other: List<T>): boolean {
+    if (!other) return false;
+    if (this.constructor !== other.constructor) return false;
+    if (this._valid !== other.valid) return false;
+    return JSON.stringify(this._value) === JSON.stringify(other.value); // crude equality check for objects, might need refinement.
+  }
+}