dotnet-csharp-modern-patterns

Name: dotnet-csharp-modern-patterns
Author: wshaddix

65stars10forks

How to install dotnet-csharp-modern-patterns?

wshaddix/dotnet-skills/dotnet-csharp-modern-patterns

$npx -y skills add wshaddix/dotnet-skills --skill dotnet-csharp-modern-patterns

Installs into the current project.

Summary

Using records, pattern matching, primary constructors, collection expressions. C# 12-15 by TFM.

Files · 1

View on GitHub

SKILL.md

1	# dotnet-csharp-modern-patterns
2
3	Modern C# language feature guidance adapted to the project's target framework. Always run [skill:dotnet-version-detection] first to determine TFM and C# version.
4
5	Cross-references: [skill:dotnet-csharp-coding-standards] for naming/style conventions, [skill:dotnet-csharp-async-patterns] for async-specific patterns.
6
7	---
8
9	## Quick Reference: TFM to C# Version
10
11	\| TFM \| C# \| Key Language Features \|
12	\|-----\|----\|-----------------------\|
13	\| net8.0 \| 12 \| Primary constructors, collection expressions, alias any type \|
14	\| net9.0 \| 13 \| `params` collections, `Lock` type, partial properties \|
15	\| net10.0 \| 14 \| `field` keyword, extension blocks, `nameof` unbound generics \|
16	\| net11.0 \| 15 (preview) \| Collection expression `with()` arguments \|
17
18	---
19
20	## Records
21
22	Use records for immutable data transfer objects, value semantics, and domain modeling where equality is based on values rather than identity.
23
24	### Record Classes (reference type)
25
26	```csharp
27	// Positional record: concise, immutable, value equality
28	public record OrderSummary(int OrderId, decimal Total, DateOnly OrderDate);
29
30	// With additional members
31	public record Customer(string Name, string Email)
32	{
33	public string DisplayName => $"{Name} <{Email}>";
34	}
35	```
36
37	### Record Structs (value type, C# 10+)
38
39	```csharp
40	// Positional record struct: value type with value semantics
41	public readonly record struct Point(double X, double Y);
42
43	// Mutable record struct (rare -- prefer readonly)
44	public record struct MutablePoint(double X, double Y);
45	```
46
47	### When to Use Records vs Classes
48
49	\| Use Case \| Prefer \|
50	\|----------\|--------\|
51	\| DTOs, API responses \| `record` \|
52	\| Domain value objects (Money, Email) \| `readonly record struct` \|
53	\| Entities with identity (User, Order) \| `class` \|
54	\| High-throughput, small data \| `readonly record struct` \|
55	\| Inheritance needed \| `record` (class-based) \|
56
57	### Non-destructive Mutation
58
59	```csharp
60	var updated = order with { Total = order.Total + tax };
61	```
62
63	---
64
65	## Primary Constructors (C# 12+, net8.0+)
66
67	Capture constructor parameters directly in the class/struct body. Parameters become available throughout the type but are not fields or properties -- they are captured state.
68
69	### For Services (DI injection)
70
71	```csharp
72	public class OrderService(IOrderRepository repo, ILogger<OrderService> logger)
73	{
74	public async Task<Order> GetAsync(int id)
75	{
76	logger.LogInformation("Fetching order {OrderId}", id);
77	return await repo.GetByIdAsync(id);
78	}
79	}
80	```
81
82	### Gotchas
83
84	- Primary constructor parameters are mutable captures, not `readonly` fields. If immutability matters, assign to a `readonly` field in the body.
85	- Do not use primary constructors when you need to validate parameters at construction time -- use a traditional constructor with guard clauses instead.
86	- For records, positional parameters become public properties automatically. For classes/structs, they remain private captures.
87
88	```csharp
89	// Explicit readonly field when immutability matters
90	public class Config(string connectionString)
91	{
92	private readonly string _connectionString = connectionString
93	?? throw new ArgumentNullException(nameof(connectionString));
94	}
95	```
96
97	---
98
99	## Collection Expressions (C# 12+, net8.0+)
100
101	Unified syntax for creating collections with `[...]`.
102
103	```csharp
104	// Array
105	int[] numbers = [1, 2, 3];
106
107	// List
108	List<string> names = ["Alice", "Bob"];
109
110	// Span
111	ReadOnlySpan<byte> bytes = [0x00, 0xFF];
112
113	// Spread operator
114	int[] combined = [..first, ..second, 99];
115
116	// Empty collection
117	List<int> empty = [];
118	```
119
120	### Collection Expression with Arguments (C# 15 preview, net11.0+)
121
122	Specify capacity, comparers, or other constructor arguments:
123
124	```csharp
125	// Capacity hint
126	List<int> nums = [with(capacity: 1000), ..Generate()];
127
128	// Custom comparer
129	HashSet<string> set = [with(comparer: StringComparer.OrdinalIgnoreCase), "Alice", "bob"];
130
131	// Dictionary with comparer
132	Dictionary<string, int> map = [with(comparer: StringComparer.OrdinalIgnoreCase),
133	new("key1", 1), new("key2", 2)];
134	```
135
136	> net11.0+ only. Requires `<LangVersion>preview</LangVersion>`. Do not use on earlier TFMs.
137
138	---
139
140	## Pattern Matching
141
142	### Switch Expressions (C# 8+)
143
144	```csharp
145	string GetDiscount(Customer customer) => customer switch
146	{
147	{ Tier: "Gold", YearsActive: > 5 } => "30%",
148	{ Tier: "Gold" } => "20%",
149	{ Tier: "Silver" } => "10%",
150	_ => "0%"
151	};
152	```
153
154	### List Patterns (C# 11+)
155
156	```csharp
157	bool IsValid(int[] data) => data is [> 0, .., > 0]; // first and last positive
158
159	string Describe(int[] values) => values switch
160	{
161	[] => "empty",
162	[var single] => $"single: {single}",
163	[var first, .., var last] => $"range: {first}..{last}"
164	};
165	```
166
167	### Type and Property Patterns
168
169	```csharp
170	decimal CalculateShipping(object package) => package switch
171	{
172	Letter { Weight: < 50 } => 0.50m,
173	Parcel { Weight: v

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dotnet-csharp-modern-patterns

65stars10forks

View on GitHub

How to install dotnet-csharp-modern-patterns?

wshaddix/dotnet-skills/dotnet-csharp-modern-patterns

$npx -y skills add wshaddix/dotnet-skills --skill dotnet-csharp-modern-patterns

Installs into the current project.

Summary

Using records, pattern matching, primary constructors, collection expressions. C# 12-15 by TFM.

Files · 1

View on GitHub

SKILL.md

1	# dotnet-csharp-modern-patterns
2
3	Modern C# language feature guidance adapted to the project's target framework. Always run [skill:dotnet-version-detection] first to determine TFM and C# version.
4
5	Cross-references: [skill:dotnet-csharp-coding-standards] for naming/style conventions, [skill:dotnet-csharp-async-patterns] for async-specific patterns.
6
7	---
8
9	## Quick Reference: TFM to C# Version
10
11	\| TFM \| C# \| Key Language Features \|
12	\|-----\|----\|-----------------------\|
13	\| net8.0 \| 12 \| Primary constructors, collection expressions, alias any type \|
14	\| net9.0 \| 13 \| `params` collections, `Lock` type, partial properties \|
15	\| net10.0 \| 14 \| `field` keyword, extension blocks, `nameof` unbound generics \|
16	\| net11.0 \| 15 (preview) \| Collection expression `with()` arguments \|
17
18	---
19
20	## Records
21
22	Use records for immutable data transfer objects, value semantics, and domain modeling where equality is based on values rather than identity.
23
24	### Record Classes (reference type)
25
26	```csharp
27	// Positional record: concise, immutable, value equality
28	public record OrderSummary(int OrderId, decimal Total, DateOnly OrderDate);
29
30	// With additional members
31	public record Customer(string Name, string Email)
32	{
33	public string DisplayName => $"{Name} <{Email}>";
34	}
35	```
36
37	### Record Structs (value type, C# 10+)
38
39	```csharp
40	// Positional record struct: value type with value semantics
41	public readonly record struct Point(double X, double Y);
42
43	// Mutable record struct (rare -- prefer readonly)
44	public record struct MutablePoint(double X, double Y);
45	```
46
47	### When to Use Records vs Classes
48
49	\| Use Case \| Prefer \|
50	\|----------\|--------\|
51	\| DTOs, API responses \| `record` \|
52	\| Domain value objects (Money, Email) \| `readonly record struct` \|
53	\| Entities with identity (User, Order) \| `class` \|
54	\| High-throughput, small data \| `readonly record struct` \|
55	\| Inheritance needed \| `record` (class-based) \|
56
57	### Non-destructive Mutation
58
59	```csharp
60	var updated = order with { Total = order.Total + tax };
61	```
62
63	---
64
65	## Primary Constructors (C# 12+, net8.0+)
66
67	Capture constructor parameters directly in the class/struct body. Parameters become available throughout the type but are not fields or properties -- they are captured state.
68
69	### For Services (DI injection)
70
71	```csharp
72	public class OrderService(IOrderRepository repo, ILogger<OrderService> logger)
73	{
74	public async Task<Order> GetAsync(int id)
75	{
76	logger.LogInformation("Fetching order {OrderId}", id);
77	return await repo.GetByIdAsync(id);
78	}
79	}
80	```
81
82	### Gotchas
83
84	- Primary constructor parameters are mutable captures, not `readonly` fields. If immutability matters, assign to a `readonly` field in the body.
85	- Do not use primary constructors when you need to validate parameters at construction time -- use a traditional constructor with guard clauses instead.
86	- For records, positional parameters become public properties automatically. For classes/structs, they remain private captures.
87
88	```csharp
89	// Explicit readonly field when immutability matters
90	public class Config(string connectionString)
91	{
92	private readonly string _connectionString = connectionString
93	?? throw new ArgumentNullException(nameof(connectionString));
94	}
95	```
96
97	---
98
99	## Collection Expressions (C# 12+, net8.0+)
100
101	Unified syntax for creating collections with `[...]`.
102
103	```csharp
104	// Array
105	int[] numbers = [1, 2, 3];
106
107	// List
108	List<string> names = ["Alice", "Bob"];
109
110	// Span
111	ReadOnlySpan<byte> bytes = [0x00, 0xFF];
112
113	// Spread operator
114	int[] combined = [..first, ..second, 99];
115
116	// Empty collection
117	List<int> empty = [];
118	```
119
120	### Collection Expression with Arguments (C# 15 preview, net11.0+)
121
122	Specify capacity, comparers, or other constructor arguments:
123
124	```csharp
125	// Capacity hint
126	List<int> nums = [with(capacity: 1000), ..Generate()];
127
128	// Custom comparer
129	HashSet<string> set = [with(comparer: StringComparer.OrdinalIgnoreCase), "Alice", "bob"];
130
131	// Dictionary with comparer
132	Dictionary<string, int> map = [with(comparer: StringComparer.OrdinalIgnoreCase),
133	new("key1", 1), new("key2", 2)];
134	```
135
136	> net11.0+ only. Requires `<LangVersion>preview</LangVersion>`. Do not use on earlier TFMs.
137
138	---
139
140	## Pattern Matching
141
142	### Switch Expressions (C# 8+)
143
144	```csharp
145	string GetDiscount(Customer customer) => customer switch
146	{
147	{ Tier: "Gold", YearsActive: > 5 } => "30%",
148	{ Tier: "Gold" } => "20%",
149	{ Tier: "Silver" } => "10%",
150	_ => "0%"
151	};
152	```
153
154	### List Patterns (C# 11+)
155
156	```csharp
157	bool IsValid(int[] data) => data is [> 0, .., > 0]; // first and last positive
158
159	string Describe(int[] values) => values switch
160	{
161	[] => "empty",
162	[var single] => $"single: {single}",
163	[var first, .., var last] => $"range: {first}..{last}"
164	};
165	```
166
167	### Type and Property Patterns
168
169	```csharp
170	decimal CalculateShipping(object package) => package switch
171	{
172	Letter { Weight: < 50 } => 0.50m,
173	Parcel { Weight: v

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