Omit trailing undefined #6652
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Omit trailing undefined #6652
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zth
commented
Feb 26, 2024
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| SomeModule.formatDate(new Date()); | ||
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| SomeModule.formatDate(new Date(), { | ||
| someOption: true | ||
| }); | ||
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| var x = SomeModule.formatDate(new Date(), undefined, true); |
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Note the difference of these 3. The first one has 2 optional args omitted, and because of that get no undefineds. The second one has the last optional arg omitted, and because of that skips the trailing undefined too.
The third call has the last optional arg set, and therefore gets undefined in between so the args end up in the right positions.
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This is great! |
cristianoc
approved these changes
Feb 27, 2024
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Superseded by #6653 (I messed up git) |
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Fixes #6543
This omits trailing
undefinedswhen applying external functions with optional arguments, when the optional argument itself is not provided (or isNone). Only applies to external calls, because that's the only place where it could matter.Some more background: ReScript v11 with uncurried mode allows us to write much more ergonomic external function bindings because we can have optional arguments where we don't need a trailing unit to apply the function itself. But, this comes with a potential problem. All arguments, whether they're actually supplied or not, would be printed as
undefinedin the resulting JS. External JS calls might care about the number of args sent into it, sosomeJsFn(1)andsomeJsFn(1, undefined)is not always treated the same. Several JS APIs can break if provided the wrong amount of arguments unless intended.cc @cristianoc what do you think about this?