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Description
Compiling the following code
func test<T>(make: () -> [T], consume: (T) -> Void) {
consume(make()[0])
}
func main() {
test(make: { () -> [Int] // in
print("hi")
return [3]
}, consume: { _ in
print("bye")
})
}leads to the following diagnostics:
<source>:6:18: warning: expression of type '(() -> [Int]).Type' is unused
test(make: { () -> [Int] // in
^~~~~~~~~~~
<source>:6:18: error: expected member name or constructor call after type name
test(make: { () -> [Int] // in
^
<source>:6:28: note: use '.self' to reference the type object
test(make: { () -> [Int] // in
^
( ).self
(thanks, swift.godbolt.org)
This is not a great error message for several reasons:
- "constructor" instead of "initializer"
- Function types don't currently have members or initializers anyway
- A function type as the first statement in a closure without a signature is probably intended to be a signature
With parameters, we get different poor errors:
x -> Int, (x) -> Int
func test<T>(make: (Int) -> [T], consume: (T) -> Void) {
consume(make(1)[0])
}
func main() {
test(make: { x -> [Int] // in
print("hi")
return [3]
}, consume: { _ in
print("bye")
})
}<source>:6:18: error: cannot find 'x' in scope
test(make: { x -> [Int] // in
^
<source>:6:18: error: expected type before '->'
test(make: { x -> [Int] // in
^
<source>:6:5: error: type of expression is ambiguous without more context
test(make: { x -> [Int] // in
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(x: Int) -> Int
func test<T>(make: (Int) -> [T], consume: (T) -> Void) {
consume(make(1)[0])
}
func main() {
test(make: { (x: Int) -> [Int] // in
print("hi")
return [3]
}, consume: { _ in
print("bye")
})
}<source>:6:16: error: contextual type for closure argument list expects 1 argument, which cannot be implicitly ignored
test(make: { (x: Int) -> [Int] // in
^
_ in
x, y -> Int
func test<T>(make: (Int, Int) -> [T], consume: (T) -> Void) {
consume(make(1, 2)[0])
}
func main() {
test(make: { x, y -> [Int] // in
print("hi")
return [3]
}, consume: { _ in
print("bye")
})
}<source>:6:19: error: consecutive statements on a line must be separated by ';'
test(make: { x, y -> [Int] // in
^
;
<source>:6:19: error: expected expression
test(make: { x, y -> [Int] // in
^
<source>:6:18: error: cannot find 'x' in scope
test(make: { x, y -> [Int] // in
^
(x, y) -> Int
func test<T>(make: (Int, Int) -> [T], consume: (T) -> Void) {
consume(make(1, 2)[0])
}
func main() {
test(make: { (x, y) -> [Int] // in
print("hi")
return [3]
}, consume: { _ in
print("bye")
})
}<source>:6:19: error: cannot find 'x' in scope
test(make: { (x, y) -> [Int] // in
^
<source>:6:22: error: cannot find 'y' in scope
test(make: { (x, y) -> [Int] // in
^
<source>:6:18: error: expected type before '->'
test(make: { (x, y) -> [Int] // in
^
<source>:6:5: error: type of expression is ambiguous without more context
test(make: { (x, y) -> [Int] // in
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(x: Int, y: Int) -> Int
func test<T>(make: (Int, Int) -> [T], consume: (T) -> Void) {
consume(make(1, 2)[0])
}
func main() {
test(make: { (x: Int, y: Int) -> [Int] // in
print("hi")
return [3]
}, consume: { _ in
print("bye")
})
}<source>:6:16: error: contextual type for closure argument list expects 2 arguments, which cannot be implicitly ignored
test(make: { (x: Int, y: Int) -> [Int] // in
^
_,_ in