Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Type Checking Extracted Methods   Many object-oriented dynamic languages allow programmers to _extract methods_
from objects and treat them as functions. This allows for flexible programming
patterns, but presents challenges for type systems. In particular, a simple
treatment of method extraction would require methods to be contravariant in the
receiver type, making overriding all-but-impossible. We present a detailed
investigation of this problem, as well as an implemented and evaluated
solution. Method extraction is a feature of many dynamically-typed and
gradually-typed languages, ranging from Python and PHP to Flow and TypeScript.
In these languages, the underlying representation of objects as records of
procedures can be accessed, and the procedures that implement methods can be
reified as functions that can be called independently. In many of these
languages, the programmer can then explicitly specify the `this` value to be
used when the method implementation is called. Unfortunately, as we show,
existing gradual type systems such as TypeScript and Flow are unsound in the
presence of method extraction. The problem for typing any such system is that
the flexibility it allows must be tamed by requiring a connection between the
object the method was extracted from, and the function value that is later
called. In Racket, where a method extraction-like facility, dubbed "structure
type properties", is fundamental to classes, generic methods, and other APIs,
these same challenges arise, and must be solved to support this feature in
Typed Racket. We show how to combine two existing type system features --
existential types and occurrence typing -- to produce a sound approach to
typing method extraction. We formalize our design, extending an existing formal
model of the Typed Racket type system, and prove that our extension is sound.
Our design is also implemented in the released version of Racket, and is
compatible with all existing Typed Racket packages, many of which already used
a previous version of this feature.

11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: bayes-an
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The categories of this paper are: physics
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: stat
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The categories of this paper are: cond-mat
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg