add a simple default-enabled autovivification feature #18650
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All current features are compile-time, so this hasn't been an issue, but my current implementation of the autovivification issue checks features at runtime, which failed to work correctly if non-bundle features were set.
This throws an error instead of performing autovivification when the feature is disabled.
Grinnz
reviewed
Mar 18, 2021
| default, but can be turned off to disable it. | ||
| This feature is available under this name from Perl 5.34 onwards, in | ||
| previous versions it was simple on all the time. |
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Personally, I expected this to work like |
Yeah. I'm not sure we really need this feature, but fatal non-autovivification is definitely not something I think we need. |
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I was mostly thinking of it as a strictness check, throwing when perl would otherwise autovivify, as if the variable was a nil object or similar. I've made this PR draft for now. |
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Unlike other features, the work for this is done at runtime, but we only get to this point when autovivification is needed, so I expect the total cost is small enough not to matter.
The only real way to eliminate all the cost would be to have alternate ops that don't autovivify, since an op flag would have about the same runtime cost.
The runtime-ness of this feature revealed a bug in my original work that reflected feature changes to %^H to PL_compiling.cop_features - the cop_features value wasn't being copied to the next/dbstate op. This was (fortunately) harmless since current features only work at compile-time (using PL_compiling), and other feature tests that anyone outside of core might want to do need to check the hinthash value from caller().