V8_WARN_UNUSED_RESULT on DefineOwnProperty?

[Mark Logan]

I'm migrating some code to v8 5.0.71 (node v6.1.0), and replacing deprecated calls to ForceSet with DefineOwnProperty/CreateDataProperty.

I'm a little confused as to why V8_WARN_UNUSED_RESULT is present in these declarations, when it wasn't present for ForceSet. Is there some new reason why I should not ignore the return value? Or, is ignoring the return value from DefineOwnProperty (or CreateDataProperty) no more dangerous than it was to ignore the return value from ForceSet?

Thanks,

Mark

[Ben Noordhuis]

I believe V8_WARN_UNUSED_RESULT didn't exist when ForceSet() was
added. Ignoring the return value is probably no more dangerous, but:

1. DefineOwnProperty() fails when you try to set a property with a
setter that throws an exception.

2. CreateDataProperty() and DefineOwnProperty() fail when the target
object is not configurable, not extensible, frozen or sealed.

IOW, there are quite a few failure modes. You almost always want to
check whether the operation succeeded and did what you thought it did.

[Jochen Eisinger]

The reason we added V8_WARN_UNUSED_RESULT was that ignoring an exception will lead to lots of unexpected and hard to debug behavior. This annotation helps embedders to not miss any place where you have to check for an exception.

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