Don’t believe everything you learn

A minute always has 60 seconds, right? Wrong! Ok, but a country always has a capital city, right? Wrong again!

Come and join us for a lighthearted talk about some of the common falsehoods that developers believe which cause issues in real, production systems. We’ll cover the classics like timezones and names, as well as some new contenders such as geography and software versions.

Transcript

1. THINGS THAT WE BELIEVE ARE TRUE…
2. THINGS THAT WE BELIEVE ARE TRUE… But they’re not
3. Falsehoods programmers believe about X
4. “Constraints placed upon a complex system by a mixture of ignorance, apathy, business requirements, or other legal constraints”
5. Hello! I’M MICHAEL I’ve made lots of mistakes in the past You can find me at @mheap
6. TIME
7. The number of days in every month starts with a 3, so either 30 or 31? February has 28
8. Each month has the same number of days every year though? February has 29 in Leap Years
9. But we can calculate the leap years - they're every 4 years? Yes... unless its divisible by 100
10. But that rules holds all the time right? Yes… unless you’re Sweden
11. But we’re agreed, February is 28 or 29 days? Yes… unless you’re Sweden
12. But we’re agreed, February is 28 or 29 days? Or the Soviet Union
13. If we ignore Sweden, Leap Years are easy. Every 4 years unless it divides by 100 …unless it doesn’t divide by 400. 1900 wasn’t a leap year, neither is 2100 2000 is.
14. It's a good job that only small companies and independent programmers have issues with leap years though…. right? https://azure.microsoft.com/en-us/blog/ summary-of-windows-azure-service- disruption-on-feb-29th-2012/
15. TIME
16. A month starts and ends in the same year Unless you’re an ancient Roman
17. A month starts and ends in the same year Or modern Ethiopian
18. Time always goes forwards Unless you’re in Shanghai 1927-12-31 23:54:08 happened twice
19. MODERN TIME
20. The day before Saturday is always Friday. Unless you’re in Samoa in 2011
21. The offsets between two time zones will remain constant. 10 changes in 2016 2 so far this year
22. If they do change there’ll be plenty of notice North Korea gave 8 days' notice of a 30 minute change in their time zone in 2015
23. When they do change, they change by an integer number of hours UTC+04:30 Afghanistan UTC+12:45 New Zealand (Chatham Islands)
24. Ok… so 15 minutes then? That’s safe? UTC-00:25:21 - Dublin Mean Time
25. Audience Participation
26. When are there more or less than 24 hours in a day? Daylight savings time! Means 23 or 25 hours in a day
27. Is the time 23:59:60 invalid? When leap seconds are inserted, a minute will be 61 seconds long.
28. NAMES Michael
29. A child will have the same surname as either their mother or father (or both) Not in Iceland
30. People have at least two names Teller (of Penn and Teller fame) Akihito (Emperor of Japan)
31. However many names they have... People’s names do not contain numbers John5… but that’s a stage name
32. However many names they have... People’s names do not contain numbers How about K8lyn? (Kaitlyn) Ok.. it was actually KVIIIlyn
33. For every rule you come up with there are guaranteed to be hundreds of exceptions
34. For every rule you come up with there are guaranteed to be hundreds of exceptions No spaces van Buren
35. For every rule you come up with there are guaranteed to be hundreds of exceptions Only letters O’Reilly
36. For every rule you come up with there are guaranteed to be hundreds of exceptions One capital letter McDonald
37. Audience Participation Michael
38. “A name must contain one or more alphanumeric characters”
40. I can safely assume that this dictionary of bad words contains no names in it.
41. I can safely assume that this dictionary of bad words contains no names in it. Ever been to Middlesex?
42. I can safely assume that this dictionary of bad words contains no names in it. Or eaten Shitake mushrooms?
43. I can safely assume that this dictionary of bad words contains no names in it. Been named Craig Cockburn?
44. I can safely assume that this dictionary of bad words contains no names in it. Or Linda Callahan?
45. What about less obvious ones? Super Bowl XXX?
46. Planning permission emails bouncing They talked about erection of a structure
47. The sad story of Christopher Null if lastname = null then… well, then try again with a lastname that isn’t “null.”
48. Addresses
49. When there is a building number, it will be all- numeric 1A Egmont Road, Middlesbrough, TS4 2HT
50. No buildings are numbered zero 0 Egmont Road, Middlesbrough, TS4 2HT
51. If the addresses on the left of the road are even, the addresses on the right must be odd You can have even numbers on both sides.. but that’s not the interesting part
52. Well, at least you can omit leading zeros 101 Alma St, Palo Alto - where apartments 1 and 001 were on different floors.
53. A street name won't include a number 8 Seven Gardens Burgh, Woodbridge, IP13 6SU
54. OK, but at the very least you wouldn't name a town Street Actually there's a town called Street in Somerset, UK.
55. You can't have two towns or cities with the same name in the same country The UK has three towns called Newport.
56. OK, but those cities won't have duplicate street names 10 High Street, Newport, PO30 1SS 10 High Street, Newport, NP20 1FQ 10 High Street, Newport, TF10 7AN
57. OK, but you don't get multiple postcodes per building DVLA Swansea: V5Cs are processed at SA99 1BA, Driving licences at SA99 1AB
58. But street names will be reasonably short - certainly less than 50 characters Aleja Alije Izetbegovića Prvig Predsjednika Predsjedništva Republika Bosna i Hercegovina
59. Addresses are a fixed point in space BF1 4FB
60. Concrete buildings are a fixed point in space In Zürich, a 6200 ton building was moved by 60 meters to make way for railway tracks
61. Audience Participation
62. Do all countries have a capital city? Switzerland does not. The government is currently in Bern, but the city is not the capital.
63. Commerce
64. A product has a price Products sold on auction site do not yet have a price. The moment the price is known is actually the moment the item will not be on sale anymore.
65. Except for auctioned items, products have one price Price with tax, price without tax, sale price, list price, minimum price
66. Currencies symbols uniquely identify a currency. The peso and dollar sign $ is used my many countries: USA, Cananda, Australia, Brunei, Namibia
67. Currencies have a unicode symbol that represents them The Swiss franc does not, and until 2010, neither did the India rupee
68. Audience Participation
69. Which currency does not have a three letter identifier? The Canadian dollar: CA$
70. Computers
71. “ The network is reliable. Latency is zero. Bandw idth is infinite. The network is secure. T opology doesn't change. There is one administrator. T ransport cost is zero. The network is homogeneous.
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73. In Summary Computers are hard Humans make assumptions Things are never as simple as they seem. Ask questions, find out more. It’ll make life easier in the long run
74. Thanks! I’M MICHAEL You can find me at @mheap