use functions for closures

after aController.swift

import UIKit
import Siesta

class LoginOrSignupViewController: UIViewController {

    @IBAction func logIn() {
        let user = User(email: emailTextField.text!, password: passwordTextField.text!, name: nameTextField?.text)
        api.login(user)
            .onSuccess(weak(self, type(of: self).transitionToApp))
            .onFailure(weak(self, type(of: self).showError))
    }

}

before aController.swift

import UIKit
import Siesta

class LoginOrSignupViewController: UIViewController {

    @IBAction func logIn() {
      let user = User(email: emailTextField.text!, password: passwordTextField.text!, name: nameTextField?.text)
      api.login(user)
          .onSuccess { [weak self] in self?.transitionToApp() }
          .onFailure { [weak self] error in self?.showError(error) }
    }
}

weakWrapper.swift

/**
 use instance functions as closures for completion blocks
 - Parameters:
 - obj: object to reference weakly
 - block: object function with arguments to use as a completion with the same arguments

 e.g. onFailure(weak(self, type(of: self).onFailure)

 */
public func weak<T: AnyObject>(_ obj: T, _ block:@escaping (T) -> () -> Void) -> () -> Void {
    return { [weak obj] in obj.map {block($0)()} }
}