Trust Your Code - Don't Be Defensive 2019-09-14

Trust Your Code - Don't defend it.

We are trained to code defensively.
We have to defend our method against getting a bad result as a return argument.
We have to defend their method from being called when it shouldn't.
We have to defend ourselves against being passed unusable parameter.

We are so focused on defending and trying to know how everything our method uses works that we become numb to the damage we're inflicting on the source code itself.

Let's trust our code.
Let's trust the return value is something we can use.
Let's trust the method knows if it should execute or not.
Let's trust that the parameter we're given is usable.

Trusting our code simplifies our code.

This trust isn't free.
This trust takes discipline and rigor.
This trust takes practices that allow us to have this trust.

This talk is about the practices that enable us to trust our code and not be so defensive about it.

1. Trust Your Code @TheQuinnGil QuinnGil.com Seattle Code Camp 2019
2. Quinn Gil Software Development Coach International Speaker on Software Development Past 15 years focused on High Quality code Blog at QuinnGil.com @TheQuinnGil QuinnGil.com
3. This is for you. @TheQuinnGil QuinnGil.com
4. Trust Your Code @TheQuinnGil QuinnGil.com
5. “Untrusted Code”? @TheQuinnGil QuinnGil.com
6. Untrusted Code - Defensive Code • Defend the Method Perspective ◦ PreConditions ◦ Nulls ◦ Assertions @TheQuinnGil QuinnGil.com
7. Untrusted Code - Defenses • Defend the Method Perspective ◦ PreConditions ◦ Nulls ◦ Assertions • Defend the Caller Perspective ◦ State Verification ◦ Exception Handling ◦ OK to call @TheQuinnGil QuinnGil.com
8. Untrusted Code - Defenses • Defend the Method Perspective ◦ PreConditions ◦ Nulls ◦ Assertions • Defend the Caller Perspective ◦ State Verification ◦ Exception Handling ◦ OK to call • Defend the Using Perspective ◦ Null ◦ Ready ◦ Valid @TheQuinnGil QuinnGil.com
9. Is “Defensive Code” really that bad? @TheQuinnGil QuinnGil.com
10. Why not “Defensive Code”? • A defense somewhere is a defense everywhere @TheQuinnGil QuinnGil.com
11. Why not “Defensive Code”? • A defense somewhere is a defense everywhere • Complicates the code @TheQuinnGil QuinnGil.com
12. Why not “Defensive Code”? • A defense somewhere is a defense everywhere • Complicates the code • Higher Cognitive Load @TheQuinnGil QuinnGil.com
13. Why not “Defensive Code”? • A defense somewhere is a defense everywhere • Complicates the code • Higher Cognitive Load • Write more code @TheQuinnGil QuinnGil.com
14. Why not “Defensive Code”? • A defense somewhere is a defense everywhere • Complicates the code • Higher Cognitive Load • Write more code • Maintain more code @TheQuinnGil QuinnGil.com
15. Why not “Defensive Code”? • A defense somewhere is a defense everywhere • Complicates the code • Higher Cognitive Load • Write more code • Maintain more code • Dead Code? Undetectable? @TheQuinnGil QuinnGil.com
16. How do we protect the code? @TheQuinnGil QuinnGil.com
17. How do we protect the code? @TheQuinnGil QuinnGil.com I don’t
18. How do we protect the code? @TheQuinnGil QuinnGil.com I don’t... directly.
19. Trust Your Code with Technical Practices @TheQuinnGil QuinnGil.com
20. Trusting Your Code is Sustainable Code @TheQuinnGil QuinnGil.com
21. Sustainable Code through Technical Practices @TheQuinnGil QuinnGil.com
22. Sustainable Code through Technical Practices @TheQuinnGil QuinnGil.com
23. Sustainable Code through Technical Practices @TheQuinnGil QuinnGil.com
24. Tests @TheQuinnGil QuinnGil.com
25. Sustainable Code through Technical Practices • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection @TheQuinnGil QuinnGil.com
26. Sustainable Code through Technical Practices Isolate Their Code @TheQuinnGil QuinnGil.com • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection
27. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { HttpClient httpClient = new HttpClient(); HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
28. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { //COUPLING HttpClient httpClient = new HttpClient(); HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
29. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { //COUPLING HttpClient httpClient = new HttpClient(); //EXCEPTION HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
30. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { //COUPLING HttpClient httpClient = new HttpClient(); //EXCEPTION HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); //EXCEPTION, COUPLING JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
31. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { //COUPLING HttpClient httpClient = new HttpClient(); //EXCEPTION HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); //EXCEPTION, COUPLING JObject jsonContent = JObject.Parse(readAsStringAsync); //IMPERATIVE string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
32. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { //COUPLING HttpClient httpClient = new HttpClient(); //EXCEPTION HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); //EXCEPTION, COUPLING JObject jsonContent = JObject.Parse(readAsStringAsync); //IMPERATIVE string value = jsonContent.Value<string>("some_key"); //EXCEPTION return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
33. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { HttpClient httpClient = new HttpClient(); HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
34. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpClientBookEnd httpClient = new HttpClientFacade(); HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
35. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpClientBookEnd httpClient = new HttpClientFacade(); IHttpResponseMessageBookEnd httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
36. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpClientBookEnd httpClient = new HttpClientFacade(); IHttpResponseMessageBookEnd httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.ContentAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
37. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpResponseMessageBookEnd httpResponseMessage = await _httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.ContentAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
38. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpResponseMessageBookEnd httpResponseMessage = await _httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.ContentAsStringAsync(); IParsedObject parsedObject = _parser.Parse(readAsStringAsync); string value = parsedObject.StringValue("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
39. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpResponseMessageBookEnd httpResponseMessage = await _httpClient.SendAsync(r); IParsedObject parsedObject = await httpResponseMessage.ParsedContent(_parser); string value = parsedObject.StringValue("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
40. Technical Practices - Isolate Their Code - 3rd Party public async Task<string> NetworkCall(HttpRequestMessage r) { HttpClient httpClient = new HttpClient(); HttpResponseMessage httpResponseMessage = await httpClient.SendAsync(r); string readAsStringAsync = await httpResponseMessage.Content.ReadAsStringAsync(); JObject jsonContent = JObject.Parse(readAsStringAsync); string value = jsonContent.Value<string>("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } public async Task<string> NetworkCall(HttpRequestMessage r) { IHttpResponseMessageBookEnd httpResponseMessage = await _httpClient.SendAsync(r); IParsedObject parsedObject = await httpResponseMessage.ParsedContent(_parser); string value = parsedObject.StringValue("some_key"); return value.Contains("expected_Value") ? "Success" : "Failure"; } @TheQuinnGil QuinnGil.com
41. What Else? Technical Practices - Isolate Their Code @TheQuinnGil QuinnGil.com
42. Operating System Technical Practices - Isolate Their Code @TheQuinnGil QuinnGil.com
43. How? Technical Practices - Isolate Their Code @TheQuinnGil QuinnGil.com
44. Technical Practices - Isolate Their Code - How? internal class HttpClientFacade : IHttpClientBookEnd { private static HttpClient _testClient; #if DEBUG public static void SetTestClient(HttpClient testClient) => _testClient = testClient; #endif private readonly HttpClient _httpClient; public HttpClientFacade() : this(new HttpClient()) { } private HttpClientFacade(HttpClient httpClient) => _httpClient = httpClient; public async Task<IHttpResponseMessageBookEnd> SendRequestAsync(HttpRequestMessage msg) => new HttpResponseMessageAdapter(await HttpClient().SendAsync(msg)); private HttpClient HttpClient() => _testClient ?? _httpClient; } @TheQuinnGil QuinnGil.com
45. Technical Practices - Isolate Their Code - How? internal class HttpClientFacade : IHttpClientBookEnd { private static HttpClient _testClient; #if DEBUG public static void SetTestClient(HttpClient testClient) => _testClient = testClient; #endif private readonly HttpClient _httpClient; public HttpClientFacade() : this(new HttpClient()) { } private HttpClientFacade(HttpClient httpClient) => _httpClient = httpClient; public async Task<IHttpResponseMessageBookEnd> SendRequestAsync(HttpRequestMessage msg) => new HttpResponseMessageAdapter(await HttpClient().SendAsync(msg)); private HttpClient HttpClient() => _testClient ?? _httpClient; } @TheQuinnGil QuinnGil.com
46. Technical Practices - Isolate Their Code - How? internal class HttpClientFacade : IHttpClientBookEnd { private static HttpClient _testClient; #if DEBUG public static void SetTestClient(HttpClient testClient) => _testClient = testClient; #endif private readonly HttpClient _httpClient; public HttpClientFacade() : this(new HttpClient()) { } private HttpClientFacade(HttpClient httpClient) => _httpClient = httpClient; public async Task<IHttpResponseMessageBookEnd> SendRequestAsync(HttpRequestMessage msg) => new HttpResponseMessageAdapter(await HttpClient().SendAsync(msg)); private HttpClient HttpClient() => _testClient ?? _httpClient; } @TheQuinnGil QuinnGil.com
47. Technical Practices - Isolate Their Code - How? internal class HttpClientFacade : IHttpClientBookEnd { private static HttpClient _testClient; #if DEBUG public static void SetTestClient(HttpClient testClient) => _testClient = testClient; #endif private readonly HttpClient _httpClient; public HttpClientFacade() : this(new HttpClient()) { } private HttpClientFacade(HttpClient httpClient) => _httpClient = httpClient; public async Task<IHttpResponseMessageBookEnd> SendRequestAsync(HttpRequestMessage msg) => new HttpResponseMessageAdapter(await HttpClient().SendAsync(msg)); private HttpClient HttpClient() => _testClient ?? _httpClient; } @TheQuinnGil QuinnGil.com
48. User Interface Technical Practices - Isolate Their Code @TheQuinnGil QuinnGil.com
49. Sustainable Code through Technical Practices Isolate Their Code @TheQuinnGil QuinnGil.com • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection Trust Your Code by controlling interactions with 3rd Party Code
50. Sustainable Code through Technical Practices Never `null` @TheQuinnGil QuinnGil.com • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection
51. Why? Technical Practices - Never `null` @TheQuinnGil QuinnGil.com
52. How? Technical Practices - Never `null` @TheQuinnGil QuinnGil.com
53. Technical Practices - Never `null` public string CalculateThing(ICanBeNull canBeNull) { if (canBeNull == null) return "Default"; IAlsoNull alsoNull = canBeNull.Example(); if (alsoNull == null) return "Default"; string sample = alsoNull.Sample(); if (sample == null) return "Default"; return sample; } @TheQuinnGil QuinnGil.com
54. Technical Practices - Never `null` public string CalculateThing(ICanBeNull canBeNull) { if (canBeNull == null) return "Default"; IAlsoNull alsoNull = canBeNull.Example(); if (alsoNull == null) return "Default"; string sample = alsoNull.Sample(); if (sample == null) return "Default"; return sample; } public string CalculateThing(ICanBeNull canBeNull) { return canBeNull?.Example()?.Sample() ?? "Default"; } @TheQuinnGil QuinnGil.com
55. Technical Practices - Never `null` public string CalculateThing(ICanBeNull canBeNull) { if (canBeNull == null) return "Default"; IAlsoNull alsoNull = canBeNull.Example(); if (alsoNull == null) return "Default"; string sample = alsoNull.Sample(); if (sample == null) return "Default"; return sample; } public string CalculateThing(ICanBeNull canBeNull) { return canBeNull?.Example()?.Sample() ?? "Default"; } public string CalculateThing(ICanNotBeNull canNotBeNull) { return canNotBeNull.Example().Sample(); } @TheQuinnGil QuinnGil.com
56. Technical Practices - Never `null` public string CalculateThing(ICanBeNull canBeNull) { if (canBeNull == null) return "Default"; IAlsoNull alsoNull = canBeNull.Example(); if (alsoNull == null) return "Default"; string sample = alsoNull.Sample(); if (sample == null) return "Default"; return sample; } public string CalculateThing(ICanBeNull canBeNull) { return canBeNull?.Example()?.Sample() ?? "Default"; } public string CalculateThing(ICanNotBeNull canNotBeNull) { return canNotBeNull.Example().Sample(); } public void Foo() { string thing = _bar.CalculateThing(_canBeNull); //... } @TheQuinnGil QuinnGil.com
57. Technical Practices - Never `null` public string CalculateThing(ICanBeNull canBeNull) { if (canBeNull == null) return "Default"; IAlsoNull alsoNull = canBeNull.Example(); if (alsoNull == null) return "Default"; string sample = alsoNull.Sample(); if (sample == null) return "Default"; return sample; } public string CalculateThing(ICanBeNull canBeNull) { return canBeNull?.Example()?.Sample() ?? "Default"; } public string CalculateThing(ICanNotBeNull canNotBeNull) { return canNotBeNull.Example().Sample(); } public void Foo() { string thing = _bar.CalculateThing(_canBeNull); //... } public void Foo() { string thing = _canNotBeNull.Example().Sample(); //... } @TheQuinnGil QuinnGil.com
58. Technical Practices - Never `null` public class NullObject : ICanNotBeNull { public IAlsoNotNull Example() => new NullObjectAlso(); } public class NullObjectAlso : IAlsoNotNull { public string Sample() => "Default"; } public string CalculateThing(ICanBeNull canBeNull) { if (canBeNull == null) return "Default"; IAlsoNull alsoNull = canBeNull.Example(); if (alsoNull == null) return "Default"; string sample = alsoNull.Sample(); if (sample == null) return "Default"; return sample; } public void Foo() { string thing = _canNotBeNull.Example().Sample(); //... } @TheQuinnGil QuinnGil.com
59. Sustainable Code through Technical Practices Never `null` @TheQuinnGil QuinnGil.com • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection Trust Your Code by always having valid objects
60. Sustainable Code through Technical Practices No Primitives @TheQuinnGil QuinnGil.com • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection
61. Primitives? Technical Practices - No Primitives @TheQuinnGil QuinnGil.com
62. Technical Practices - What are Primitives? • Data (string, int, double, float, ...) @TheQuinnGil QuinnGil.com
63. Technical Practices - What are Primitives? • Data (string, int, double, float, ...) • Collections (List, Map, Dictionary, ...) @TheQuinnGil QuinnGil.com
64. Technical Practices - What are Primitives? • Data (string, int, double, float, ...) • Collections (List, Map, Dictionary, ...) • Enums @TheQuinnGil QuinnGil.com
65. Technical Practices - What are Primitives? • Data (string, int, double, float, ...) • Collections (List, Map, Dictionary, ...) • Enums • More? @TheQuinnGil QuinnGil.com
66. Why not Primitives? Technical Practices - No Primitives @TheQuinnGil QuinnGil.com
67. • Object oriented programming wants object interaction, not data manipulation Technical Practices - Why No Primitives? @TheQuinnGil QuinnGil.com
68. • Object oriented programming wants object interaction, not data manipulation • Primitives are data, not objects Technical Practices - Why No Primitives? @TheQuinnGil QuinnGil.com
69. • Object oriented programming wants object interaction, not data manipulation • Primitives are data, not objects • Primitives force complex imperative code Technical Practices - Why No Primitives? @TheQuinnGil QuinnGil.com
70. • Object oriented programming wants object interaction, not data manipulation • Primitives are data, not objects • Primitives force complex imperative code • Primitives hinder Emergent Design Technical Practices - Why No Primitives? @TheQuinnGil QuinnGil.com
71. • Object oriented programming wants object interaction, not data manipulation • Primitives are data, not objects • Primitives force complex imperative code • Primitives hinder Evolutionary Architecture • Primitives limit use of Design Patterns Technical Practices - Why No Primitives? @TheQuinnGil QuinnGil.com
72. Instead? Technical Practices - No Primitives @TheQuinnGil QuinnGil.com
73. Represent the Concept Technical Practices - No Primitives @TheQuinnGil QuinnGil.com
74. Technical Practices - No Primitives - Age Example public bool ThirteenOrLess(DataPerson person) { DateTime birthDate = DateTime.Parse(person.BirthDate); int age = DateTime.Now.Year - birthDate.Year; /* is this right?*/ return age <= 13; } @TheQuinnGil QuinnGil.com
75. public bool ThirteenOrLess(DataPerson person) { DateTime birthDate = DateTime.Parse(person.BirthDate); int age = DateTime.Now.Year - birthDate.Year; if (birthDate.Date > DateTime.Now.AddYears(-age)) age--; return age <= 13; } @TheQuinnGil QuinnGil.com Technical Practices - No Primitives - Age Example
76. public bool ThirteenOrLess(DataPerson person) { DateTime birthDate = DateTime.Parse(person.BirthDate); int age = DateTime.Now.Year - birthDate.Year; if (birthDate.Date > DateTime.Now.AddYears(-age)) age--; switch (person.State) { case "WA": return age <= 13; case "AK": return age <= 14; } return false; } @TheQuinnGil QuinnGil.com Technical Practices - No Primitives - Age Example
77. public bool IsMinor(DataPerson person) { DateTime birthDate = DateTime.Parse(person.BirthDate); int age = DateTime.Now.Year - birthDate.Year; if (birthDate.Date > DateTime.Now.AddYears(-age)) age--; switch (person.State) { case "WA": return age <= 13; case "AK": return age <= 14; } return false; } @TheQuinnGil QuinnGil.com Technical Practices - No Primitives - Age Example
78. public class Age : IAge { public bool IsMinor() { DateTime birthDate = DateTime.Parse(_birthdate); int age = DateTime.Now.Year - birthDate.Year; if (birthDate.Date > DateTime.Now.AddYears(-age)) age--; switch (_state) { case "WA": return age <= 13; case "AK": return age <= 14; } return false; } } @TheQuinnGil QuinnGil.com Technical Practices - No Primitives - Age Example
79. public class Age : IAge { public bool IsMinor() { DateTime birthDate = DateTime.Parse(_birthdate); int age = DateTime.Now.Year - birthDate.Year; if (birthDate.Date > DateTime.Now.AddYears(-age)) age--; switch (_state) { case "WA": return age <= 13; case "AK": return age <= 14; } return false; } } public class Person { private readonly string _birthdate; private readonly string _state; public IAge Age() => new Age(_birthdate, _state); } @TheQuinnGil QuinnGil.com Technical Practices - No Primitives - Age Example
80. public class Age : IAge { public bool IsMinor() { DateTime birthDate = DateTime.Parse(_birthdate); int age = DateTime.Now.Year - birthDate.Year; if (birthDate.Date > DateTime.Now.AddYears(-age)) age--; return age <= _state.MinorAge(); } } public class Person { private readonly string _birthdate; private readonly State _state; public IAge Age() => new Age(_birthdate, _state); } @TheQuinnGil QuinnGil.com Technical Practices - No Primitives - Age Example
81. Technical Practices - No Primitives - Age Example @TheQuinnGil QuinnGil.com Represent the Concept
82. Technical Practices - No Primitives - Units public float Convert(float value) @TheQuinnGil QuinnGil.com
83. Technical Practices - No Primitives - Units public float Convert(float value) { return value * 1.609334f; } @TheQuinnGil QuinnGil.com
84. Technical Practices - No Primitives - Units public float Convert(float value) { return value * 1.609334f; } Money? @TheQuinnGil QuinnGil.com
85. Technical Practices - No Primitives - Units public float Convert(float value) { return value * 1.609334f; } Money? Distance? @TheQuinnGil QuinnGil.com
86. Technical Practices - No Primitives - Units public float Convert(float value) { return value * 1.609334f; } @TheQuinnGil QuinnGil.com Money? Distance? Convert To? From?
87. Technical Practices - No Primitives - Units public float Convert(float distance) { return distance * 1.609334f; } Missing Meta Data Convert To? From? @TheQuinnGil QuinnGil.com Money? Distance?
88. Technical Practices - No Primitives - Units public class Distance ... distance.ToKilometer(); ... With Meta Data @TheQuinnGil QuinnGil.com
89. Technical Practices - No Primitives - Age Example @TheQuinnGil QuinnGil.com Represent the Concept
90. Sustainable Code through Technical Practices No Primitives @TheQuinnGil QuinnGil.com Trust Your Code by having objects represent the concepts in the code • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection
91. Sustainable Code through Technical Practices @TheQuinnGil QuinnGil.com • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection
92. Feature Parity in 25% of the Dev Hours @TheQuinnGil QuinnGil.com
93. THANK YOU! @TheQuinnGil QuinnGil.com
94. Sustainable Code through Technical Practices • No Getters / No Setters • `if` Only As Guard Clause • Isolate Their Code • Never `null` • No `new` inline • Composition, Not Inheritance • <Strong opinions loosely held> • Be Immutable • No Primitives • Extract Cohesion • No Public Statics • Never Reflection @TheQuinnGil QuinnGil.com