2,569 research outputs found
The C++0x "Concepts" Effort
C++0x is the working title for the revision of the ISO standard of the C++
programming language that was originally planned for release in 2009 but that
was delayed to 2011. The largest language extension in C++0x was "concepts",
that is, a collection of features for constraining template parameters. In
September of 2008, the C++ standards committee voted the concepts extension
into C++0x, but then in July of 2009, the committee voted the concepts
extension back out of C++0x.
This article is my account of the technical challenges and debates within the
"concepts" effort in the years 2003 to 2009. To provide some background, the
article also describes the design space for constrained parametric
polymorphism, or what is colloquially know as constrained generics. While this
article is meant to be generally accessible, the writing is aimed toward
readers with background in functional programming and programming language
theory. This article grew out of a lecture at the Spring School on Generic and
Indexed Programming at the University of Oxford, March 2010
Ramsey expansions of metrically homogeneous graphs
We discuss the Ramsey property, the existence of a stationary independence
relation and the coherent extension property for partial isometries (coherent
EPPA) for all classes of metrically homogeneous graphs from Cherlin's
catalogue, which is conjectured to include all such structures. We show that,
with the exception of tree-like graphs, all metric spaces in the catalogue have
precompact Ramsey expansions (or lifts) with the expansion property. With two
exceptions we can also characterise the existence of a stationary independence
relation and the coherent EPPA.
Our results can be seen as a new contribution to Ne\v{s}et\v{r}il's
classification programme of Ramsey classes and as empirical evidence of the
recent convergence in techniques employed to establish the Ramsey property, the
expansion (or lift or ordering) property, EPPA and the existence of a
stationary independence relation. At the heart of our proof is a canonical way
of completing edge-labelled graphs to metric spaces in Cherlin's classes. The
existence of such a "completion algorithm" then allows us to apply several
strong results in the areas that imply EPPA and respectively the Ramsey
property.
The main results have numerous corollaries on the automorphism groups of the
Fra\"iss\'e limits of the classes, such as amenability, unique ergodicity,
existence of universal minimal flows, ample generics, small index property,
21-Bergman property and Serre's property (FA).Comment: 57 pages, 14 figures. Extends results of arXiv:1706.00295. Minor
revisio
Projective geometries arising from Elekes-Szab\'o problems
We generalise the Elekes-Szab\'o theorem to arbitrary arity and dimension and
characterise the complex algebraic varieties without power saving. The
characterisation involves certain algebraic subgroups of commutative algebraic
groups endowed with an extra structure arising from a skew field of
endomorphisms. We also extend the Erd\H{o}s-Szemer\'edi sum-product phenomenon
to elliptic curves. Our approach is based on Hrushovski's framework of
pseudo-finite dimensions and the abelian group configuration theorem.Comment: 48 pages. Minor improvements in presentation. To appear in ASEN
Geographical Indications: The Economics of Claw-Back
Geographical Indications (GIs) for products (Basmati rice, Champagne sparkling wine, Antigua coffee, etc.) were regulated at the international level in 1995 (WTO TRIPS Agreement, Part II, Section 3). This paper proposes a model on the welfare effects of the socalled “claw-back” of GIs; i.e. the protection in a country (Home) of a GI of another country (Foreign), when the said GI had previously acquired generic status at Home (cf.: protection of Feta in the EU or of Champagne in Chile). The setting includes two countries (Home and Foreign); three varieties (Foreign GI-original goods, Home GI-variety goods and generics) and a continuum of heterogeneous consumers. Two regimes are analyzed: protection / no protection; in two scenarios for Foreign firms: perfect / oligopolistic competition. Only the equilibrium at Home is analyzed. Although a loss in global welfare is always expected when fewer varieties are available in a market, results suggest that industrialized Home countries, with sophisticated consumers and higher relative costs tend to lose less from protecting Foreign GIs than developing Home countries, where the opposite is true. With oligopolistic competition, GI firms become from differentiated from their closest competitor after protection (now generics), further stressing the competitive distortion; consumers with a low willingness to pay for origin and a high degree of valuation for the GI-variety are the biggest losers. Regarding firms, however, contrary to the conventional wisdom, oligopolistic competition by Foreign firms leads to less stringent conditions for Home GI-varieties to compete, and does not affect generics. In effect, if after protection Home GI-varieties can successfully differentiate themselves from Foreign GI-original goods without the (unlawful) use of the GI label (either through the development of their own GI or through proper branding) and stay competitive, the scenario of oligopolistic competition from Foreign firms is more favorable to their development than the scenario of perfect competition.
Generics, Race, and Social Perspectives
The project of this paper is to deliver a semantics for a broad subset of bare plural generics about racial kinds, a class which I will dub 'Type C generics.' Examples include 'Blacks are criminal' and 'Muslims are terrorists.' Type C generics have two interesting features. First, they link racial kinds with ​ socially perspectival predicates ​ (SPPs). SPPs lead interpreters to treat the relationship between kinds and predicates in generic constructions as nomic or non-accidental. Moreover, in computing their content, interpreters must make implicit reference to socially privileged​ ​ perspectives which are treated as authoritative about whether a given object fits into the extension of the predicate. Such deference grants these authorities influence over both the conventional meaning of these terms and over the nature of the ​ objects ​ in the social ontology that these terms purport to describe, much the way a baseball umpire is authoritative over the meaning and metaphysics of 'strike'/​ strike ​. Second, terms like 'criminal' and 'terrorist' receive default ​ racialized ​ interpretations in which these terms conventionally token racial or ethnic identities. I show that neither of these features can be explained by Sarah-Jane Leslie's influential 'weak semantics' for generics, and show how my own 'socially perspectival semantics' fares better on both counts. Finally, I give an analysis of 'Blacks are criminal' which explores the semantic mechanisms that underlie default racialized interpretations
Geographical Indications: The Economics of Claw-Back
Graduate Institute of International and Development Studies Working Paper No: 11/2010International Relations/Trade,
C++ Standard Template Library by template specialized containers
The C++ Standard Template Library is the flagship example for libraries based
on the generic programming paradigm. The usage of this library is intended to
minimize the number of classical C/C++ errors, but does not warrant bug-free
programs. Furthermore, many new kinds of errors may arise from the inaccurate
use of the generic programming paradigm, like dereferencing invalid iterators
or misunderstanding remove-like algorithms. In this paper we present some
typical scenarios that may cause runtime or portability problems. We emit
warnings and errors while these risky constructs are used. We also present a
general approach to emit "customized" warnings. We support the so-called
"believe-me marks" to disable warnings. We present another typical usage of our
technique, when classes become deprecated during the software lifecycle
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