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Patterns and enums #1460

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merged 3 commits into from
Feb 28, 2024
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Patterns and enums #1460

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eada9ba
Say that Struct patterns can match enum values
mattheww Jan 29, 2024
c6049ba
Cover enums in the refutability rule for tuple struct patterns
mattheww Jan 29, 2024
08e5cd4
Say that struct patterns can match union values
mattheww Feb 27, 2024
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20 changes: 16 additions & 4 deletions src/patterns.md
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Expand Up @@ -597,8 +597,8 @@ Reference patterns are always irrefutable.
[_OuterAttribute_]: attributes.md
[TUPLE_INDEX]: tokens.md#tuple-index

Struct patterns match struct values that match all criteria defined by its subpatterns.
They are also used to [destructure](#destructuring) a struct.
Struct patterns match struct and enum values that match all criteria defined by its subpatterns.
They are also used to [destructure](#destructuring) a struct or enum value.
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Can this also include union?

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I've added that


On a struct pattern, the fields are referenced by name, index (in the case of tuple structs) or ignored by use of `..`:

Expand Down Expand Up @@ -628,6 +628,18 @@ match t {
PointTuple {0: 10, ..} => (),
PointTuple {..} => (),
}

# enum Message {
# Quit,
# Move { x: i32, y: i32 },
# }
# let m = Message::Quit;
#
match m {
Message::Quit => (),
Message::Move {x: 10, y: 20} => (),
Message::Move {..} => (),
}
```

If `..` is not used, it is required to match all fields:
Expand Down Expand Up @@ -662,7 +674,7 @@ The `ref` and/or `mut` _IDENTIFIER_ syntax matches any value and binds it to a v
let Struct{a: x, b: y, c: z} = struct_value; // destructure all fields
```

A struct pattern is refutable when one of its subpatterns is refutable.
A struct pattern is refutable if the _PathInExpression_ resolves to a constructor of an enum with more than one variant, or one of its subpatterns is refutable.

## Tuple struct patterns

Expand All @@ -676,7 +688,7 @@ A struct pattern is refutable when one of its subpatterns is refutable.
Tuple struct patterns match tuple struct and enum values that match all criteria defined by its subpatterns.
They are also used to [destructure](#destructuring) a tuple struct or enum value.

A tuple struct pattern is refutable when one of its subpatterns is refutable.
A tuple struct pattern is refutable if the _PathInExpression_ resolves to a constructor of an enum with more than one variant, or one of its subpatterns is refutable.

## Tuple patterns

Expand Down