Hello,

I'm running into an issue memoizing a getter that relies on configuration set in the constructor. It appears that this line in memDecorator calls the getter immediately in addition to retrieving the getter function:

const input = target[propertyKey]; // eslint-disable-line @typescript-eslint/no-unsafe-assignment

Example:

import { memDecorator } from 'mem'

export class TestMemoizeGetter {
  constructorCalled?: boolean

  constructor() {
    this.constructorCalled = true
  }

  @memDecorator()
  public get someGetter() {
    if (!this.constructorCalled) {
      throw new Error('constructor has not been called')
    }

    return Math.random()
  }
}

const instance = new TestMemoizeGetter()

assert.doesNotThrow(() => {
  const value = instance.someGetter
  assert.strictEqual(instance.someGetter, value)
})

Output:

Error: constructor has not been called
    at Object.get someGetter (/home/neodon/p/mem-getters/index.ts:14:13)
    at file:///home/neodon/p/mem-getters/node_modules/mem/dist/index.js:84:29
    at __decorateClass (file:///home/neodon/p/mem-getters/index.ts:1:374)
    at <anonymous> (/home/neodon/p/mem-getters/index.ts:12:14)
    at ModuleJob.run (node:internal/modules/esm/module_job:194:25)

I messed around with the implementation for memDecorator and had some luck by using descriptor.value for functions and descripter.get for getter functions. It created some more problems though around this bindings. It seems that getter functions have a lot of voodoo baked in.

Let me know if you see value in this getting fixed. I can create a pull request with a failing test, and add some of the partial fix I figured out.

Also, the same issue exists with p-memoize, but it seemed better to start here since getters are synchronous.