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[wildcard-variables] Clarify wildcard behaviour on functions. #3813

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May 17, 2024
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[wildcard-variables] Clarify wildcard behaviour on functions. #3813

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23 changes: 12 additions & 11 deletions working/wildcards/feature-specification.md
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Original file line number Diff line number Diff line change
Expand Up @@ -76,21 +76,21 @@ library privacy comes into play.

## Proposal

### Local declarations
### Declarations that are capable of declaring a wildcard

A *local declaration* is any of:
Any of the following kinds of declarations can declare a wildcard:

* Function parameters. This includes top-level functions, local functions,
function expressions ("lambdas"), instance methods, static methods,
constructors, etc. It includes all parameter kinds: simple, field formals,
and function-typed formals, etc.:
constructors, etc. It includes all parameter kinds, excluding named
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I want to explicitly call this out. Not sure if this is the best place to write this. I know it's in Initializing formals, but it'd be nice to restate here.

parameters: simple, field formals, and function-typed formals, etc.:

```dart
Foo(_, this._, super._, void _(), {_}) {}
Foo(_, this._, super._, void _()) {}

list.where((_) => true);

void f(void g(_, _)) {}
void f(void g(int _, bool _)) {}

typedef T = void Function(String _, String _);
```
Expand Down Expand Up @@ -130,8 +130,8 @@ A *local declaration* is any of:
takeGenericCallback(<_>() => true);
```

A local declaration whose name is `_` does not bind that name to anything. This
means you can have multiple local declarations named `_` in the same namespace
A declaration whose name is `_` does not bind that name to anything. This
means you can have multiple declarations named `_` in the same namespace
without a collision error. The initializer, if there is one, is still executed,
but the value is not accessible.

Expand All @@ -153,12 +153,13 @@ Named fields of record types are unchanged. It is still a compile-time error for

```dart
void f() {
_() {} // Error.
_(); // Error.
_() {} // Dead code.
_(); // Error, not in scope.
}
```

It's an error to declare a local function declaration named `_`.
A local function declaration named `_` is dead code and will produce a warning
because the function is unreachable.

### Other declarations

Expand Down