🔒 ERC-20 Decimals Implementation

[jaglinux]

https://github.com/pcaversaccio/snekmate/blob/main/src/tokens/ERC20.vy#L78 is declared constant.
Is it better to declare it as immutable so that the user can set the value in constructor ? rather than changing the code.
(I guess Vyper does not support virtual / override and hence the decision to have decimals as constant.)

[jaglinux]

cc @pcaversaccio

[pcaversaccio]

@jaglinux thanks for starting this discussion - when I was writing the code for the ERC20 contract I thought about it very properly (immutable vs. constant) and decided to choose constant for the following reasons:

• I want to enforce the standard 18 decimals if possible. Decimals can be very confusing and need special care from certain protocols if a token does not adhere to the 18 decimals. Two famous examples that do not conform with the norm of 18 decimals are USDC & USDT. That caused more trouble than good IMHO.
• The most common Solidity library OpenZeppelin does default to 18 (a counter-example would be Solmate which uses an immutable variable) even though it's a virtual function (a feature that Vyper does not support). So if you want to override it, you must do the following for example:

/// @dev Overrides the `decimals` function to use the custom value of 6.
function decimals() public view virtual override returns (uint8) {
    return 6;
}

If you do this, you (should) know what you're doing. And the same holds for my ERC20 version - if you want to implement decimals as an immutable variable, you can simply do this by adjusting the code. But first, you must understand the code (as well as the implications) and that is what I want to achieve 😀.

[jaglinux]

@pcaversaccio Thanks for detailed explanation.
Yeah, I was referring to USDC wherein the decimal is different than 18.
As you mentioned, the OZ implementation requires the user to explicitly override the decimals() and in snekmate implementation the user need to explicitly modify the code. (fair enough)
For the record, Solmate implements decimals as immutable. It also forces user to specify in the constructor always. If it's gonna be 18 most of the times ,then this can be overhead.

[pcaversaccio]

It's pretty simple - if people want to modify the code, they must perfectly understand the code & consequences. And that's what I want to achieve.

[pcaversaccio]

UPDATE: I made decimals an immutable variable via #234, which will be shipped via the 0.1.0 release that targets Vyper version 0.4.0.