Use SnapKit with the Facebook Pop animation framework. Inspired from MSSPopMasonry
Open your project in Xcode, then drag 'POP+SnapKit.swift' onto your project (use the "Product Navigator view"). Make sure to select Copy items when asked if you extracted the code archive outside of your project.
circle.snp_makeConstraints { make in
self.radiusConstaint = make.width.equalTo(self.radius * 2).constraint
}
let spring = POPSpringAnimation(propertyNamed: kPOPLayoutConstraintConstant)
spring.toValue = newValue * 2
self.radiusConstaint?.layoutConstraint?.pop_addAnimation(spring, forKey: "someKey")