dart-use-pattern-matching

Name: dart-use-pattern-matching
Author: flutter

789installs159forks

How to install dart-use-pattern-matching?

flutter/agent-plugins/dart-use-pattern-matching

$npx -y skills add flutter/agent-plugins --skill dart-use-pattern-matching

Installs into the current project.

Summary

Use switch expressions and pattern matching where appropriate

Files · 1

View on GitHub

SKILL.md

1	# Implementing Dart Patterns
2
3	## Contents
4	- [Pattern Selection Strategy](#pattern-selection-strategy)
5	- [Switch Statements vs. Expressions](#switch-statements-vs-expressions)
6	- [Core Pattern Implementations](#core-pattern-implementations)
7	- [Workflows](#workflows)
8	- [Examples](#examples)
9
10	## Pattern Selection Strategy
11
12	Apply specific pattern types based on the data structure and desired outcome. Follow these conditional guidelines:
13
14	* If validating and extracting from deserialized data (e.g., JSON): Use Map and List patterns to simultaneously check structure and destructure key-value pairs.
15	* If handling multiple return values: Use Record patterns to destructure fields directly into local variables.
16	* If executing type-specific behavior (Algebraic Data Types): Use Object patterns combined with `sealed` classes to ensure exhaustiveness.
17	* If matching numeric ranges or conditions: Use Relational (`>=`, `<=`) and Logical-and (`&&`) patterns.
18	* If multiple cases share logic: Use Logical-or (`\|\|`) patterns to share a single case body or guard clause.
19	* If ignoring specific values: Use the Wildcard pattern (`_`) or a non-matching Rest element (`...`) in collections.
20
21	## Switch Statements vs. Expressions
22
23	Select the appropriate switch construct based on the execution context:
24
25	* If producing a value: Use a switch expression.
26	* Syntax: `switch (value) { pattern => expression, }`
27	* Rule: Each case must be a single expression. No implicit fallthrough. Must be exhaustive.
28	* If executing statements or side effects: Use a switch statement.
29	* Syntax: `switch (value) { case pattern: statements; }`
30	* Rule: Empty cases fall through to the next case. Non-empty cases implicitly break (no `break` keyword required).
31
32	## Core Pattern Implementations
33
34	Implement patterns using the following syntax and rules:
35
36	* Logical-or (`\|\|`): `pattern1 \|\| pattern2`. Both branches must define the exact same set of variables.
37	* Logical-and (`&&`): `pattern1 && pattern2`. Branches must not define overlapping variables.
38	* Relational: `==`, `!=`, `<`, `>`, `<=`, `>=` followed by a constant expression.
39	* Cast (`as`): `pattern as Type`. Throws if the value does not match the type. Use to forcibly assert types during destructuring.
40	* Null-check (`?`): `pattern?`. Fails the match if the value is null. Binds the variable to the non-nullable base type.
41	* Null-assert (`!`): `pattern!`. Throws if the value is null.
42	* Variable: `var name` or `Type name`. Binds the matched value to a new local variable.
43	* Wildcard (`_`): Matches any value and discards it.
44	* List: `[pattern1, pattern2]`. Matches lists of exact length unless a Rest element (`...` or `...var rest`) is used.
45	* Map: `{"key": pattern}`. Matches maps containing the specified keys. Ignores unmatched keys.
46	* Record: `(pattern1, named: pattern2)`. Matches records of the exact shape. Use `:var name` to infer the getter name.
47	* Object: `ClassName(field: pattern)`. Matches instances of `ClassName`. Use `:var field` to infer the getter name.
48
49	## Workflows
50
51	### Task Progress: Implementing Pattern Matching
52	Copy this checklist to track progress when implementing complex pattern matching logic:
53
54	- [ ] Identify the data structure being evaluated (JSON, Record, Class, Enum).
55	- [ ] Select the appropriate switch construct (Expression for values, Statement for side-effects).
56	- [ ] Define the required patterns (Object, Map, List, Record).
57	- [ ] Extract required data using Variable patterns (`var x`, `:var y`).
58	- [ ] Apply Guard clauses (`when condition`) for logic that cannot be expressed via patterns.
59	- [ ] Handle unmatched cases using a Wildcard (`_`) or `default` clause (if not using a sealed class).
60	- [ ] Run exhaustiveness validator.
61
62	### Feedback Loop: Exhaustiveness Checking
63	When switching over `sealed` classes or enums, you must ensure all subtypes are handled.
64
65	1. Run validator: Execute `dart analyze`.
66	2. Review errors: Look for "The type 'X' is not exhaustively matched by the switch cases" errors.
67	3. Fix: Add the missing Object patterns for the unhandled subtypes, or add a Wildcard (`_`) case if a default fallback is acceptable.
68
69	## Examples
70
71	### JSON Validation and Destructuring
72	Use Map and List patterns to validate structure and extract data in a single step.
73
74	Input:
75	```dart
76	var data = {
77	'user': ['Lily', 13],
78	};
79	```
80
81	Implementation:
82	```dart
83	if (data case {'user': [String name, int age]}) {
84	print('User $name is $age years old.');
85	} else {
86	print('Invalid JSON structure.');
87	}
88	```
89
90	### Algebraic Data Types (Sealed Classes)
91	Use Object patterns with switch expressions to handle family types exhaustively.
92
93	Implementation:

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dart-use-pattern-matching

789installs159forks

View on GitHub

How to install dart-use-pattern-matching?

flutter/agent-plugins/dart-use-pattern-matching

$npx -y skills add flutter/agent-plugins --skill dart-use-pattern-matching

Installs into the current project.

Summary

Use switch expressions and pattern matching where appropriate

Files · 1

View on GitHub

SKILL.md

1	# Implementing Dart Patterns
2
3	## Contents
4	- [Pattern Selection Strategy](#pattern-selection-strategy)
5	- [Switch Statements vs. Expressions](#switch-statements-vs-expressions)
6	- [Core Pattern Implementations](#core-pattern-implementations)
7	- [Workflows](#workflows)
8	- [Examples](#examples)
9
10	## Pattern Selection Strategy
11
12	Apply specific pattern types based on the data structure and desired outcome. Follow these conditional guidelines:
13
14	* If validating and extracting from deserialized data (e.g., JSON): Use Map and List patterns to simultaneously check structure and destructure key-value pairs.
15	* If handling multiple return values: Use Record patterns to destructure fields directly into local variables.
16	* If executing type-specific behavior (Algebraic Data Types): Use Object patterns combined with `sealed` classes to ensure exhaustiveness.
17	* If matching numeric ranges or conditions: Use Relational (`>=`, `<=`) and Logical-and (`&&`) patterns.
18	* If multiple cases share logic: Use Logical-or (`\|\|`) patterns to share a single case body or guard clause.
19	* If ignoring specific values: Use the Wildcard pattern (`_`) or a non-matching Rest element (`...`) in collections.
20
21	## Switch Statements vs. Expressions
22
23	Select the appropriate switch construct based on the execution context:
24
25	* If producing a value: Use a switch expression.
26	* Syntax: `switch (value) { pattern => expression, }`
27	* Rule: Each case must be a single expression. No implicit fallthrough. Must be exhaustive.
28	* If executing statements or side effects: Use a switch statement.
29	* Syntax: `switch (value) { case pattern: statements; }`
30	* Rule: Empty cases fall through to the next case. Non-empty cases implicitly break (no `break` keyword required).
31
32	## Core Pattern Implementations
33
34	Implement patterns using the following syntax and rules:
35
36	* Logical-or (`\|\|`): `pattern1 \|\| pattern2`. Both branches must define the exact same set of variables.
37	* Logical-and (`&&`): `pattern1 && pattern2`. Branches must not define overlapping variables.
38	* Relational: `==`, `!=`, `<`, `>`, `<=`, `>=` followed by a constant expression.
39	* Cast (`as`): `pattern as Type`. Throws if the value does not match the type. Use to forcibly assert types during destructuring.
40	* Null-check (`?`): `pattern?`. Fails the match if the value is null. Binds the variable to the non-nullable base type.
41	* Null-assert (`!`): `pattern!`. Throws if the value is null.
42	* Variable: `var name` or `Type name`. Binds the matched value to a new local variable.
43	* Wildcard (`_`): Matches any value and discards it.
44	* List: `[pattern1, pattern2]`. Matches lists of exact length unless a Rest element (`...` or `...var rest`) is used.
45	* Map: `{"key": pattern}`. Matches maps containing the specified keys. Ignores unmatched keys.
46	* Record: `(pattern1, named: pattern2)`. Matches records of the exact shape. Use `:var name` to infer the getter name.
47	* Object: `ClassName(field: pattern)`. Matches instances of `ClassName`. Use `:var field` to infer the getter name.
48
49	## Workflows
50
51	### Task Progress: Implementing Pattern Matching
52	Copy this checklist to track progress when implementing complex pattern matching logic:
53
54	- [ ] Identify the data structure being evaluated (JSON, Record, Class, Enum).
55	- [ ] Select the appropriate switch construct (Expression for values, Statement for side-effects).
56	- [ ] Define the required patterns (Object, Map, List, Record).
57	- [ ] Extract required data using Variable patterns (`var x`, `:var y`).
58	- [ ] Apply Guard clauses (`when condition`) for logic that cannot be expressed via patterns.
59	- [ ] Handle unmatched cases using a Wildcard (`_`) or `default` clause (if not using a sealed class).
60	- [ ] Run exhaustiveness validator.
61
62	### Feedback Loop: Exhaustiveness Checking
63	When switching over `sealed` classes or enums, you must ensure all subtypes are handled.
64
65	1. Run validator: Execute `dart analyze`.
66	2. Review errors: Look for "The type 'X' is not exhaustively matched by the switch cases" errors.
67	3. Fix: Add the missing Object patterns for the unhandled subtypes, or add a Wildcard (`_`) case if a default fallback is acceptable.
68
69	## Examples
70
71	### JSON Validation and Destructuring
72	Use Map and List patterns to validate structure and extract data in a single step.
73
74	Input:
75	```dart
76	var data = {
77	'user': ['Lily', 13],
78	};
79	```
80
81	Implementation:
82	```dart
83	if (data case {'user': [String name, int age]}) {
84	print('User $name is $age years old.');
85	} else {
86	print('Invalid JSON structure.');
87	}
88	```
89
90	### Algebraic Data Types (Sealed Classes)
91	Use Object patterns with switch expressions to handle family types exhaustively.
92
93	Implementation:

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6 picks

Type