Default value of WebAssembly.Global

[binji]

I'm currently working on the v8 implementation of this proposal, and noticed that the current wording requires the default value of a f32 or f64 WebAssembly.Global to be NaN.

I believe this is because of the step 1. Let |v| be |descriptor|["value"], which makes |v| undefined, which ToWebAssemblyValue converts to NaN. This seems to be consistent with passing an undefined value to an exported function, but I think in this case it would be nicer to have the default be zero instead.

Note that if an imported global has an undefined in the import object, a LinkError will be thrown instead:

1. If |globaltype| is [=𝗂𝟨𝟦=] or [=Type=](|v|) is not [=Number=], throw a {{LinkError}} exception.

[lars-t-hansen]

I probably agree that zero is nicer (== more useful for more programs), but this seems like the type of case that justifies the existence of NaN in the first place.

I won't be able to attend the CG f2f next week but perhaps get this on the agenda for a quick poll?

[jfbastien]

Make sure to ask which NaN, and which zero 😉

[binji]

We discussed this at the April CG meeting, and decided to make the default value 0.

@rossberg also presented on the js types proposal, where it would be more convenient to move the value initializer out of the descriptor, into a second argument:

new WebAssembly.Global({type, mutable}, value);

This second argument, if omitted, will use the default value for the type. For the numeric types, that's 0, but for future nullable reference types it will be null.