How to use trailing closure in if condition?

Question

Here is the code:

class Person {
}

func lastNameForPerson(person: Person, caseFolding: ((String)->(String))? = nil) -> String {
    if let folder = ca         


        

Answer 1

Put your function call between parentheses:

if "SMITH" == (lastNameForPerson(Person()) {$0.uppercaseString}) {

otherwise the == operator takes precedence and the compiler evaluates it as

if ("SMITH" == lastNameForPerson(Person())) {$0.uppercaseString} {

which is not valid code.