What is the use case for convenience initializer?

Question

In swift there is the concept of designated initializer (which is the "normal" constructor we know from other languages, I assume).
But there is also something called Convenience Initializer, which I do understand how to write, but the point is lost on me.
As, If I understand correctly, you can achieve the same thing without writing the keyword convenience, or not?

Answer 1

Actually it's very easy to understand them: they are initializers with default parameters.

From the docs:

Convenience initializers are secondary, supporting initializers for a class. You can define a convenience initializer to call a designated initializer from the same class as the convenience initializer with some of the designated initializer’s parameters set to default values. You can also define a convenience initializer to create an instance of that class for a specific use case or input value type.

Example:

class A {
    var a: Int
    var b : Int

    init() {
        a = 0
        b = 0
    }

    /*convenience*/ init(a: Int) {
        self.init()
        self.a = a
    }
}

In the above case, you cannot call self.init(), you have mark your initializer with the convenience keyword, otherwise it will be a compiler error. So you cannot chain two designated initializer from the same class.

Answer 2

As I understand, the only point in those initializers is convenience. Sometimes it happens that, we often need to create some object with same arguments over and over again. In that case, we can just add another init method which takes much less parameters and the remaining ones are hard coded.

For example, some Logger class

init(type: LoggerType, filepath: String, configurations: LoggerConfig, etc.)

It might be that we often use this logger with same arguments. To avoid duplicating code, we can add a convenience initializer with some default values

convenience init(){ self.init(type: LoggerType.SomeType, filepath: "/log", configurations: LoggerConfig.Default) }