Archive for August 29, 2016

Monday, August 29, 2016

Error Handling Compared

Matt Gallagher:

The Result type is so useful that it was almost included in the Swift standard library and even its rejection reveals an interesting look at the philosophies underpinning Swift’s design.


Some implementations of Result use a generic parameter for the error […] Frankly, until Swift supports structural sum types (and there is no guarantee that it ever will), this can potentially involve a lot of manual work propagating errors to communicate a small amount of additional type information that the interface user will promptly ignore by treating all errors identically (bail out on any error).


The effect of Swift’s error handling over successive throws statements is equivalent to the monadic flatMap over multiple Result generating functions but Swift avoids making abstract mathematical concepts like map and flatMap a required part of the core language and instead makes the code look as though it is a simple, linear sequence of actions.

Matt Gallagher:

Given that all of the Swift compiler developers are themselves C++ developers, it is interesting that Swift has turned out almost, but not quite, entirely unlike C++. While Swift’s error handling offers potentially similar control flow to C++ exceptions, C++ exceptions provided the clearest example of what the Swift developers wanted to avoid with Swift.

Swift would also rather solve problems with clear syntax rather than the numerous safe implementation rules required in C++. The defer syntax used to manage cleanup at scope exit, including around thrown errors, is an example of language syntax avoiding the need for safe implementation rules like RAII.


However, Haskell’s approach to error handling does have some limitations. Specifically, monadic handling makes it very easy to “bind” (>>=) to get the “success” result and totally ignore what happens in an error case. Monadic handling encourages the ignoring of errors. If this code had omitted the catch handling, the IO monad would have propagated all the way to the output of the main function.

There’s also an almost total lack of signalling. Unless you look for the bind operator, do notation or the catch, return or fail functions, it’s difficult to know where IO or other monads are involved. Haskell’s pervasive type inferencing is often a hindrance here: only one of these functions is required to actually specify a type signature.


While Swift has copied some of the syntactic elements of [Java] checked exceptions, Swift is very careful to avoid calling its errors “exceptions” since they are different in important ways. Most significantly, Swift’s errors are as performant as returning an error code and have no overlap with technology intended for fatal errors.

Tricking Facial Recognition With 3D Rendering

Lily Hay Newman:

Earlier this month at the Usenix security conference, security and computer vision specialists from the University of North Carolina presented a system that uses digital 3-D facial models based on publicly available photos and displayed with mobile virtual reality technology to defeat facial recognition systems. A VR-style face, rendered in three dimensions, gives the motion and depth cues that a security system is generally checking for. The researchers used a VR system shown on a smartphone’s screen for its accessibility and portability.

Their attack, which successfully spoofed four of the five systems they tried, is a reminder of the downside to authenticating your identity with biometrics. By and large your bodily features remain constant, so if your biometric data is compromised or publicly available, it’s at risk of being recorded and exploited. Faces plastered across the web on social media are especially vulnerable—look no further than the wealth of facial biometric data literally called Facebook.

mov Is Turing-complete

Stephen Dolan (PDF, via Emily St.):

It is well-known that the x86 instruction set is baroque, overcomplicated, and redundantly redundant. We show just how much fluff it has by demonstrating that it remains Turing-complete when reduced to just one instruction.

The instruction we choose is mov, which can do both loads and stores. We use no unusual addressing modes, self-modifying code, or runtime code generation. Using just this instruction (and a single unconditional branch at the end of the program to make nontermination possible), we demonstrate how an arbitrary Turing machine can be simulated.


The M/o/Vfuscator (short ‘o’, sounds like “mobfuscator”) compiles programs into “mov” instructions, and only “mov” instructions. Arithmetic, comparisons, jumps, function calls, and everything else a program needs are all performed through mov operations; there is no self-modifying code, no transport-triggered calculation, and no other form of non-mov cheating.

Update (2016-08-29): Rosyna Keller:

As is xor

What I Learned From 10 Years of Doing PR for Apple

Cameron Craig:

We didn’t work with long media lists. Instead, we focused on a relatively small number of reporters who we believed set the tone for others to follow. We’d offer these reporters such things as exclusive interviews, following a launch or first shot at reviewing new products. By keeping the number small, our hands-on approach was more manageable. After the initial coverage from influencers, we’d expand our reach to regional reporters and trade publications.


Most importantly, respect your brand. That’s the biggest lesson of all that I learned at Apple. It’s your biggest asset and you have to protect it. Think twice before giving away your products in a raffle. Think carefully about what other brands you associate with.