Software. Is

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Lester Strickland
5 years ago
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1 Software Is

4 Any program is a model of a model within a theory of a model of an abstraction of some portion of the world or of some universe of discourse. Meir M Lehman "Programs, Life Cycles, and Laws of Software Evolution"

5 The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise. Edsger W Dijkstra

7 Details count. Peter Weinberger

8 Geeks are people who love something so much that all the details matter. Marissa Mayer

9 We're talking about a very specific mindset that is crucial when it comes to the act of creating. Will Gompertz Think Like an Artist

10 It is an attitude that can be encapsulated in a simple but demanding rule: always think both big picture and fine detail. Will Gompertz Think Like an Artist

11 software

12 software architecture

13 code

14 implementation

15 implementation details

16 design details

17 design decisions

19 Architecture represents the significant design decisions that shape a system, where significant is measured by cost of change. Grady Booch

20 We propose [...] that one begins with a list of difficult design decisions or design decisions which are likely to change. Each module is then designed to hide such a decision from the others. David L Parnas On the Criteria to Be Used in Decomposing Systems into Modules

21 Programming is a design activity. Jack W Reeves What Is Software Design?

22 Coding actually makes sense more often than believed. Often the process of rendering the design in code will reveal oversights and the need for additional design effort. The earlier this occurs, the better the design will be. Jack W Reeves What Is Software Design?

24 If a plot works out exactly as you first planned, you're not working loosely enough to give room to your imagination and instincts.

25 / WordFriday

26 pantser, noun Writer who writes by the seat of their pants. In contrast to a plotter, a pantser doesn't work to (or have) an outline.

29 16-bit

30 32-bit

31 64-bit

32 <windows.h>

33 LLP64

34 LP64

35 Ophelia: 'Tis in my memory locked, and you yourself shall keep the key of it. William Shakespeare The Tragedy of Hamlet [Act I, Scene 3]

36 Hamlet: Yea, from the table of my memory I'll wipe away all trivial fond records. William Shakespeare The Tragedy of Hamlet [Act I, Scene 5]

38 Unshared mutable data needs no synchronisation Unshared Mutable Shared mutable data needs synchronisation Shared Unshared immutable data needs no synchronisation Immutable Shared immutable data needs no synchronisation

39 Mutable The Synchronisation Quadrant Unshared mutable data needs no synchronisation Unshared Shared mutable data needs synchronisation Shared Unshared immutable data needs no synchronisation Immutable Shared immutable data needs no synchronisation

41 All computers wait at the same speed

42 Savings in time feel like simplicity

43 ... premature optimization is the root of all evil (or at least most of it) in programming. Donald Knuth

44 ... premature optimization is the root of all evil (or at least most of it) in programming. Donald Knuth

45 ... premature optimization is the root of all evil (or at least most of it) in programming. Donald Knuth

46 Command-line tools can be 235x faster than your Hadoop cluster Adam Drake

47 sort

49 O(n log n)

50 O(n 2 )

53 O(n!)

55 OMG!

57 O(n)

59 Remember that there is no code faster than no code. Taligent's Guide to Designing Programs

60 Write code that is easy to delete, not easy to extend.

63 function leftpad (str, len, ch) { str = String(str); var i = -1; if (!ch && ch!== 0) ch = ' '; len = len - str.length; while (++i < len) { str = ch + str; } } return str;

64 zfill

65 rjust

66 var cache = [ '', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ' ]; function leftpad (str, len, ch) { // convert `str` to `string` str = str + ''; // `len` is the `pad`'s length now len = len - str.length; // doesn't need to pad if (len <= 0) return str; // `ch` defaults to `' '` if (!ch && ch!== 0) ch = ' '; // convert `ch` to `string` ch = ch + ''; // cache common use cases if (ch === ' ' && len < 10) return cache[len] + str; // `pad` starts with an empty string var pad = ''; // loop while (true) { // add `ch` to `pad` if `len` is odd if (len & 1) pad += ch; // divide `len` by 2, ditch the remainder len >>= 1; // "double" the `ch` so this operation count grows logarithmically on `len` // each time `ch` is "doubled", the `len` would need to be "doubled" too // similar to finding a value in binary search tree, hence O(log(n)) if (len) ch += ch; // `len` is 0, exit the loop else break; } // pad `str`! return pad + str; }

67 I have yet to see any problem, however complicated, which, when you looked at it in the right way, did not become still more complicated. Anderson's Law

68 function leftpad(content, length, pad) { content = String(content) pad = String(pad pad === 0? pad : ' ')[0] var left = Math.max(length - content.length, 0) return pad.repeat(left) + content }

69 test({ "Padding an empty string to a length of 0 results in an empty string": () => assert(leftpad("", 0, "X") === ""), "Padding a non-empty string to a shorter length results in the same string": () => assert(leftpad("foobar", 3, "X") === "foobar"), "Padding a non-empty string to a negative length results in the same string": () => assert(leftpad("foobar", -3, "X") === "foobar"), "Padding a non-empty string to its length results in the same string": () => assert(leftpad("foobar", 6, "X") === "foobar"), "Padding to a longer length with a single character fills to the left": () => assert(leftpad("foobar", 8, "X") === "XXfoobar"), "Padding to a longer length with surplus characters fills using only first": () => assert(leftpad("foobar", 10, "XY") === "XXXXfoobar"), "Padding to a longer length with an empty string fills with space": () => assert(leftpad("foobar", 8, "") === " foobar"), "Padding to a longer length with no specified fill fills with space": () => assert(leftpad("foobar", 9) === " foobar"), "Padding to a longer length with integer 0 fills with 0": () => assert(leftpad("foobar", 7, 0) === "0foobar"), "Padding to a longer length with single-digit integer fills with digit": () => assert(leftpad("foobar", 10, 1) === "1111foobar"), "Padding to a longer length with multiple-digit integer fills with first digit": () => assert(leftpad("foobar", 10, 42) === "4444foobar"), "Padding to a longer length with negative integer fills with -": () => assert(leftpad("foobar", 8, -42) === "--foobar"), "Padding a non-string uses string representation": () => assert(leftpad(4.2, 5, 0) === "004.2") })

70 function assert(condition) { if(!condition) throw { name: "AssertionError", message: "assertion failed" } } function testpasses(totry) { try { totry() return true } catch (failure) { return false } } function report(testname, passed) { document.write(testname.fontcolor(passed? "green" : "red") + "<br>") } function test(testcases) { for (var testname in testcases) if (testcases.hasownproperty(testname)) report(testname, testpasses(testcases[testname])) }

71 Padding an empty string to a length of 0 results in an empty string Padding a non-empty string to a shorter length results in the same string Padding a non-empty string to a negative length results in the same string Padding a non-empty string to its length results in the same string Padding to a longer length with a single character fills to the left Padding to a longer length with surplus characters fills using only first Padding to a longer length with an empty string fills with space Padding to a longer length with no specified fill fills with space Padding to a longer length with integer 0 fills with 0 Padding to a longer length with single-digit integer fills with digit Padding to a longer length with multiple-digit integer fills with first digit Padding to a longer length with negative integer fills with - Padding a non-string uses string representation

72 Padding an empty string to a length of 0 results in an empty string Padding a non-empty string to a shorter length results in the same string Padding a non-empty string to a negative length results in the same string Padding a non-empty string to its length results in the same string Padding to a longer length with a single character fills to the left Padding to a longer length with surplus characters fills using only first Padding to a longer length with an empty string fills with space Padding to a longer length with no specified fill fills with space Padding to a longer length with integer 0 fills with 0 Padding to a longer length with single-digit integer fills with digit Padding to a longer length with multiple-digit integer fills with first digit Padding to a longer length with negative integer fills with - Padding a non-string uses string representation

73 Simple Testing Can Prevent Most Critical Failures An Analysis of Production Failures in Distributed Data-Intensive Systems

75 Schiaparelli s Inertial Measurement Unit (IMU) went about its business of calculating the lander s rotation rate. For some reason, the IMU calculated a saturationmaximum period that persisted for one second longer than what would normally be expected at this stage. When the IMU sent this bogus information to the craft s navigation system, it calculated a negative altitude.

76 That fateful miscalculation set off a cascade of despair, triggering the premature release of the parachute and the backshell, a brief firing of the braking thrusters, and activation of the on-ground systems as if Schiaparelli had already reached the surface. This all happened while the vehicle was still two miles (3.7 km) above ground.

77 A majority of the production failures (77%) can be reproduced by a unit test.

79 Your Customers Do Not Mean What They Say Nate Jackson

80 I ve never met a customer yet that wasn t all too happy to tell me what they wanted usually in great detail. The problem is that customers don t always tell you the whole truth. Nate Jackson

81 They generally don't lie. They use their terms and their contexts. They leave out significant details. They make assumptions. Nate Jackson

82 This is compounded by the fact that many customers don t actually know what they want in the first place! Nate Jackson

87 Software Is Details

Software. Is

Software. Is Software Is Details @KevlinHenney Any program is a model of a model within a theory of a model of an abstraction of some portion of the world or of some universe of discourse. Meir M Lehman "Programs,