Why createMemo is not lazy?

[Strate]

I realized that createMemo is not lazy - it calls callback as soon as createMemo defined. This leads to several inconsistenses

Current state of view might not need actual value of that memo, so computation could be defer:

const memoizedValue = createMemo(() => expensiveFunction(signal()))

<Show when={otherFlag()}>
  <div>{JSON.stringify(memoizedValue())}</div>
</Show>

In this example we do not need memoizedValue, until otherFlag() is set.

Second example is about messing with Suspenses, I extracted to playground https://playground.solidjs.com/anonymous/81480f12-9cf2-46b2-8a1e-4f98917b74d2
tldr: using createMemo could implicitly trigger resource to load, resulting in triggering unexpected Suspense boundary

What is the reason for making createMemo eager instead of lazy?

[kachurun]

Same question here. Expected behavior is the same as mobx.computed, but I'm getting these really expensive computations on init because it's not lazy.

[kachurun]

So I've just done this custom lazyMemo:

import { createMemo } from 'solid-js';
import type { Accessor, EffectFunction, NoInfer } from 'solid-js';

export function lazyMemo<Next extends Prev, Prev = Next>(
    fn: EffectFunction<undefined | NoInfer<Prev>, Next>
): Accessor<Next | undefined>;

export function lazyMemo<Next extends Prev, Init = Next, Prev = Next>(
    fn: EffectFunction<Init | Prev, Next>,
    value?: Init
): Accessor<Next | undefined> {
    let memo: Accessor<Next | undefined>;

    return function() {
        memo = memo || createMemo(() => fn(value as Init));
        return memo();
    };
}

[ryansolid]

Just what I was looking at the time. I created Solid back in 2016 and was inspired heavily by S.js which was all eager. Changing to lazy would have been breaking. But it will be lazy in 2.0.