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[patterns] Change if-case statement syntax to a more infix-like form. #2191

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Apr 6, 2022
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[patterns] Change if-case statement syntax to a more infix-like form. #2191

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16 changes: 11 additions & 5 deletions working/0546-patterns/patterns-feature-specification.md
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Expand Up @@ -4,7 +4,7 @@ Author: Bob Nystrom

Status: In progress

Version 1.5 (see [CHANGELOG](#CHANGELOG) at end)
Version 1.6 (see [CHANGELOG](#CHANGELOG) at end)

Note: This proposal is broken into a couple of separate documents. See also
[records][] and [exhaustiveness][].
Expand Down Expand Up @@ -577,13 +577,13 @@ form similar to [if-case in Swift][]:
[if-case in swift]: https://useyourloaf.com/blog/swift-if-case-let/

```dart
if (case [int x, int y] = json) return Point(x, y);
if (json case [int x, int y]) return Point(x, y);
```

It may have an else branch as well:

```dart
if (case [int x, int y] = json) {
if (json case [int x, int y]) {
print('Was coordinate array $x,$y');
} else {
throw FormatException('Invalid JSON.');
Expand All @@ -593,7 +593,7 @@ if (case [int x, int y] = json) {
The grammar is:

```
ifCaseStatement ::= 'if' '(' 'case' matcher '=' expression ')'
ifCaseStatement ::= 'if' '(' expression 'case' matcher ')'
statement ('else' statement)?
```

Expand Down Expand Up @@ -1104,7 +1104,7 @@ is the non-nullable base type of the nullable value being matched:

```dart
String? maybeString = ...
if (case var s? = maybeString) {
if (maybeString case var s?) {
// s has type String here.
}
```
Expand Down Expand Up @@ -1873,6 +1873,12 @@ main() {

## Changelog

### 1.6

- Change syntax of if-case statement ([#2181][]).

[#2181]: https://github.com/dart-lang/language/issues/2181

### 1.5

- Introduce and clarify type inference.
Expand Down