Difference between function and closure assignment

Question

Is there any difference in swift between function declaration:

func function(a: String) {
    print(a);
}
function("test");

and closure assignment:

let closure = {
    (a: String) in
    print(a);
}
closure("test");

Is there any difference between those?

Answer 1

1. Named or anonymous

   func function(a: String) {
       print("\(a), name: \(__FUNCTION__)");
   }
   
   let closure = { (a: String) in
       print("\(a), name: \(__FUNCTION__)");
   }
   

2. Capture List
   supported in closures only:

   let obj = FooClass()
   let closure = { [weak obj] in ... }
   

3. Curried function
   supported in functions only:

   func curriedFunc(x:Int)(y:Int) { ... }
   let curried = curriedFunc(1)
   curried(y:2)
   

   Similar, but not exact the same with using closure:

   let closure = { (x:Int) in { (y:Int) in ... }}
   

4. Generics
   supported in functions only:

   func function<T>(x:T) { ... }
   

5. Referenceability from its own initial declaration
   supported in global functions only:

   func recursive(var x:Int) -> Int {
       ...
       return condition ?  x : recursive(x)
   }
   

   You can do this using closure also:

   var recursive:((Int) -> Int)!
   recursive = { (var x) in
       ...
       return condition ? x : recursive(x)
   }
   

   But this is not recommended because this causes strong reference cycles.

6. Overload
   supported in functions only:

   func function(a: String) { print("String: \(a)") }
   func function(a: Float) { print("Float: \(a)") }
   

   n.b. You can reference them as a closure like this:

   let f:(Float) -> Void = function