expect | Write better assertions | Assertion library

You can use itertools.dropwhile:

References can't bind to objects with different type directly. Given const int& s = u;, u is implicitly converted to int firstly, which is a temporary, a brand-new object and then s binds to the temporary int. (Lvalue-references to const (and rvalue-references) could bind to temporaries.) The lifetime of the temporary is prolonged to the lifetime of s, i.e. it'll be destroyed when get out of main.

I suspect this may have been an accident, though I prefer the new behavior.

The new behavior is a consequence of a change to how the bytecode for * arguments works. The change is in the changelog under Python 3.9.0 alpha 3:

bpo-39320: Replace four complex bytecodes for building sequences with three simpler ones.

The following four bytecodes have been removed:

• BUILD_LIST_UNPACK
• BUILD_TUPLE_UNPACK
• BUILD_SET_UNPACK
• BUILD_TUPLE_UNPACK_WITH_CALL

The following three bytecodes have been added:

• LIST_TO_TUPLE
• LIST_EXTEND
• SET_UPDATE

On Python 3.8, the bytecode for f(*a, a.pop()) looks like this:

The evaluation order of A = B was not specified before c++17, after c++17 B is guaranteed to be evaluated before A, see https://en.cppreference.com/w/cpp/language/eval_order rule 20.

The behaviour of valMap[val] = valMap.size(); is therefore unspecified in c++14, you should use:

It's a global outage in JCenter. You can monitor status at https://status.gradle.com. It replaces the bintray status page which seems is now fully sunset and returns a 502 error.

UPDATE Jan 13, 06:35 UTC

JCenter is now back online, and systems are fully operational.

UPDATE Jan 20

Gradle Plugin resolution outage postmortem

https://blog.gradle.org/plugins-jcenter

Following this incident, the Gradle Plugin Portal now uses a JCenter mirror hosted by Gradle instead of JCenter directly. This should shield users from short JCenter outages for libraries that have been cached by the mirror. We saw another short outage of JCenter over the weekend and this did not appear to impact Gradle Plugin Portal users.

It looks like GCC's naïveté about store-forwarding stalls is hurting its auto-vectorization strategy here. See also Store forwarding by example for some practical benchmarks on Intel with hardware performance counters, and What are the costs of failed store-to-load forwarding on x86? Also Agner Fog's x86 optimization guides.

(gcc -O3 enables -ftree-vectorize and a few other options not included by -O2, e.g. if-conversion to branchless cmov, which is another way -O3 can hurt with data patterns GCC didn't expect. By comparison, Clang enables auto-vectorization even at -O2, although some of its optimizations are still only on at -O3.)

It's doing 64-bit loads (and branching to store or not) on pairs of ints. This means, if we swapped the last iteration, this load comes half from that store, half from fresh memory, so we get a store-forwarding stall after every swap. But bubble sort often has long chains of swapping every iteration as an element bubbles far, so this is really bad.

(Bubble sort is bad in general, especially if implemented naively without keeping the previous iteration's second element around in a register. It can be interesting to analyze the asm details of exactly why it sucks, so it is fair enough for wanting to try.)

Anyway, this is pretty clearly an anti-optimization you should report on GCC Bugzilla with the "missed-optimization" keyword. Scalar loads are cheap, and store-forwarding stalls are costly. (Can modern x86 implementations store-forward from more than one prior store? no, nor can microarchitectures other than in-order Atom efficiently load when it partially overlaps with one previous store, and partially from data that has to come from the L1d cache.)

Even better would be to keep buf[x+1] in a register and use it as buf[x] in the next iteration, avoiding a store and load. (Like good hand-written asm bubble sort examples, a few of which exist on Stack Overflow.)

If it wasn't for the store-forwarding stalls (which AFAIK GCC doesn't know about in its cost model), this strategy might be about break-even. SSE 4.1 for a branchless pmind / pmaxd comparator might be interesting, but that would mean always storing and the C source doesn't do that.

If this strategy of double-width load had any merit, it would be better implemented with pure integer on a 64-bit machine like x86-64, where you can operate on just the low 32 bits with garbage (or valuable data) in the upper half. E.g.,

This is what solved it for me on my M1.

1. Go to Android Studio Preview and download the latest Canary build for Apple chip (Chipmunk). Don't worry this is just to get through the initial setup.
2. Unpack it, run it, let it install all the SDK components, accept licenses, etc as usual.
3. Once it's done, simply close it and delete it.

Now when you start your stable Android Studio (Arctic Fox) you should not see the error.

You're right that a smarter compiler should be able to resolve this unambiguously.

The way Java resolves method invocations is complex. It's defined by the JLS, and I make it 7500 words purely to determine how to resolve a method. Pasted into a text editor, it was 15 pages.

The general approach is:

1. Compile-Time Step 1: Determine Type to Search (no issue here)
2. Compile-Time Step 2: Determine Method Signature
   1. Identify Potentially Applicable Methods
   2. Phase 1: Identify Matching Arity Methods Applicable by Strict Invocation
   3. Phase 2: Identify Matching Arity Methods Applicable by Loose Invocation
   4. Phase 3: Identify Methods Applicable by Variable Arity Invocation
   5. Choosing the Most Specific Method
   6. Method Invocation Type
3. Compile-Time Step 3: Is the Chosen Method Appropriate?

I don't understand anywhere close to all of the details and how it pertains to your specific case. If you care to dive into it then I've already linked the full spec. Hopefully this explanation is good enough for your purposes:

Ambiguousness is determined at step 2.6, but there is still a further appropriateness check at step 3. Your foo method must be failing at step 3. Your bar method never makes it that far because the compiler still considers both methods to be valid possibilities. A human can make the determination that the non-appropriateness resolves the ambiguity, but that's not order the compiler does things. I could only speculate why - performance might be a factor.

Your code is operating at the intersection of generics, overloading and method references, all three of which were introduced at different times; it's not massively surprising to me that the compiler would struggle.

The question is not why this fails for int[], but why it works for all the other types! Unfortunately, you have fallen prey to ADL which is actually calling std::size instead of the size function you have written. This is because all overloads of your function fail, and so it looks in the namespace of the first argument for a matching function, where it finds std::size. Rerun your program with the function renamed to something else: