Improve inferrability of stream IO #36323
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Most concrete IO types declare that a subset of their fields are other abstract IO types. As a result, if `obj1::IO`, and `obj2 = obj1.fieldwithabstracttype`, then inference has no way of knowing what type `obj2.status` returns. When `obj2.status` is used as an argument for `Base.somefunction`, this leaves such code vulnerable to invalidation via package specializations of `Base.somefunction` even when in practice there is no risk that any IO code will call the new package-supplied method. This provides a more formal interface for three non-exported abstract types: `LibuvStream`, `LibuvServer`, and `AbstractPipe`.
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If there are no objections, I might merge this soon. Among my invalidation PRs, this isn't one of the most consequential in terms of latency, but I think it has a certain elegance: it provides an example of how one might non-obtrusively define interfaces for abstract types. xref #4935 |
JeffBezanson
approved these changes
Jun 22, 2020
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A lot of IO subtypes wrap other IO objects, and the field type declaration is typically abstract (e.g.,
::IOor::LibuvStream). This leads to widespread inference problems, because it's not possible for inference to know whatio.io.statuswill return, even if it knows thatio.io::LibuvStream.To fix this, this PR defines a formal interface for three abstract types (
LibuvStream,LibuvServer, andAbstractPipe) by specializinggetpropertyfor them and adding name-specific type assertions. Since these types are unexported, it should not be considered a breaking change to specify that certain fields must have certain types.This change makes most functions in
base/stream.jlpretty well-inferred, which is a substantial change from where we are now.