Stronger enforcement of not nil and requiresInit
#13808
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Araq
reviewed
Mar 30, 2020
New issue: since `Table[A, B]` allocates its backing storage with `newSeq[KeyValuePair[A, B]]`, it's no longer legal to create a table with `not nil` types used as either keys or values.
The new mechanism can deal with more complex scenarios such as not nil field appearing in a non-default case object branch or a field within a generic object that may depend on a when branch. The commit also plugs another hole: the user is no longer able to create illegal default values through seq.setLen(N).
timotheecour
reviewed
Apr 1, 2020
timotheecour
reviewed
Apr 1, 2020
| @@ -80,7 +80,7 @@ block thashes: | |||
| # Test with range | |||
| block: | |||
| type | |||
| R = range[1..10] | |||
| R = range[0..9] | |||
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why does this test need to change?
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Because it produces a new warning, I think.
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no this PR actually suppresses the warning instead (which is great); so IMO the test should keep [1..10], and the 2 # causes warning, why? can finally disappear. yay.
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This plugs a great number of holes in the object construction and sequence growing logic preventing the creation of values that violate
not nilorrequiresInitrequirements.As the manual already states, when the
requiresInitis specified on an object type, all construction expressions needs to initialize all of the fields of the constructed type. You can also set therequiresInitpragma only on specific fields to enforce a mandatory subset.Please read the commit messages and the provided test cases for a full list of fixes and modified behaviors. I'll appreciate it if this PR is not squashed while merging, because I might need to return to specific commits to perform experiments.
One final remaining issue is that it's no longer possible to instantiate the tables and set types in the standard library with
not niltypes, becausenewSeqandseq.setLenare no longer allowed when the element type doesn't have a legal default value.My very last commits includes a demonstration how the
KeyValuePairtype can be modified to restore the full functionality, but this would come at the expense of some optimisation tricks done in tables.nim. There are some alternative solutions that may solve the problem, but require additional work.