In C++, = default and {} are not the same constructor
Comments on “In C++, = default and {} are not the same constructor”
3 judges. Scored by all three judges. Only the day’s top stories get the claim check. How far stories are checked
Daniel Lemire shows that in C++ an empty default constructor written as = default and one written as {} can differ sharply in speed. The first keeps the type trivial, while {} is user-provided and makes it non-trivial. In his span-and-box loop benchmark, GCC 15.2 and 16.2 run the = default version at about 7.75–8.04 ns per span versus 1.73 ns for {}. GCC 14.3 and clang 21 show no gap. The test covers one workload on one Xeon CPU.
Why it ranked
No. 20 of 107 with a score of 0.62. The panel rated it highest on technical depth (0.92) and new information (0.90), lowest on significance (0.45). Placed No. 20, No. 39 by score alone: the placement terms moved other stories past it.
- AI judgeJudge 2claude-haiku-5-5
- Detailed, benchmarked C++ codegen explanation showing a real performance pitfall in defaulted vs user-provided constructors; well-evidenced with compiler versions and timings, niche but practically useful to C++ builders.
- AI judgeJudge 3gpt-5.6-luna
- A technically detailed C++ semantics and compiler-codegen investigation, backed by assembly, benchmarks, compiler/version comparisons, hardware details, and reproducible code. It reveals a substantial GCC regression with actionable implications for performance-sensitive C++ code.
Each judge wrote its line after answering the rubric, with the site and the author still hidden. Every answer behind this is in the table under Score.
Score
0.62total under rubric v2.3
- Significance0.45
- Reader interest0.71
- Audience breadth0.51
- Practical relevance0.70
- Substantiated0.85
- Technical depth0.92
- New information0.90
- Counts against: Promotional0.03
- Counts against: Overclaim0.21
Each judge’s answer per question (0–1), their mean and spread, and what the question adds to the score (weight × mean).
| Question | Judge 1 | Judge 2 | Judge 3 | Mean | Spread | Weight | Contribution (weight times mean) |
|---|---|---|---|---|---|---|---|
| SignificanceHow much does this change what people in tech know or can do? | 0.50 | 0.30 | 0.54 | 0.45 | 0.24 | +0.24 | +0.107 |
| Reader interestWould a well-informed senior engineer or tech founder want to read this today, and likely pass it on? | 0.60 | 0.70 | 0.84 | 0.71 | 0.24 | +0.26 | +0.185 |
| Audience breadthHow many people who build technology does it concern? | 0.55 | 0.40 | 0.57 | 0.51 | 0.17 | +0.13 | +0.066 |
| Practical relevanceHow useful is it to someone who builds software or tech products? | 0.69 | 0.65 | 0.78 | 0.70 | 0.13 | +0.22 | +0.155 |
| SubstantiatedHow well is it backed? Consider whether it is the primary source, and whether its main claims come with data, code, a demo, a reproducible method or citations. | 0.87 | 0.80 | 0.88 | 0.85 | 0.08 | +0.05 | +0.042 |
| Technical depthHow technically substantive is it? | 0.99 | 0.90 | 0.86 | 0.92 | 0.13 | +0.05 | +0.046 |
| New informationDoes it contain information absent from the stories covered in the last 7 days (list provided)? | 0.88 | 0.90 | 0.93 | 0.90 | 0.05 | +0.05 | +0.045 |
| PromotionalIs it mainly marketing with little substance (a press release, ad or sponsored post with no real information)? A launch post that carries real news is not promotional. | 0.05 | 0.03 | 0.01 | 0.03 | 0.04 | −0.19 | −0.006 |
| OverclaimDo the headline or conclusions claim more than the body supports? | 0.36 | 0.20 | 0.08 | 0.21 | 0.28 | −0.11 | −0.023 |
| Sum of contributions | +0.618 | ||||||
| Claim-check penalty | 0.000 | ||||||
| Total, as published | 0.618 | ||||||
Spread is the highest minus the lowest judge answer. marks a spread above 0.40: the judges disagree, and the story is marked contested.
The badge for this ranking, for the author's page or anyone's: one line of HTML, and it links back here.
<a href="https://rubric.hrih.si/editions/2026-11-03/20/"><img src="https://rubric.hrih.si/badge/2026-11-03/20.svg" alt="Ranked #20 on Rubric, 3 Nov 2026" width="238" height="28"></a>Also covered by
No other coverage was clustered with this story.
Elsewhere
Elsewhere: HN 3 pts, not on front page
Recorded for context only, checked 3 Nov 2026, 05:47 UTC. It played no part in the ranking.