Which types initialise with default zero value when using a constructor in Swift?

Looking through a Swift MIDI library, I found a variable initialised like so:

var client = MIDIClientRef()

I only thought this was weird after realising that MIDIClientRef isn't a function, it's a typealias for a UInt32, so wondered why the constructor pattern is used.

So a few simple questions:

Is it common to initialise a variable like this: var myVar = Int()?
Which types initialise with a default zero value when initialised with a constructor like this?
How does it initialise with a zero value if no argument is passed in?

Looking at the public init() function in Swift.Math.Integers the comments state that it "Creates a new value equal to zero." But I couldn't find what actually creates this default value in the following code.

Solution

UInt32 conforms to the BinaryInteger protocol and that requires an init() method which “Creates a new value equal to zero.”

There is also a default implementation which can be found in Integers.swift:

extension BinaryInteger {
  /// Creates a new value equal to zero.
  @_transparent
  public init() {
    self = 0
  }

  // ...
}

Other types have explicit no-argument init methods, like all floating point types:

  @_transparent
  public init() {
    let zero: Int64 = 0
    self._value = Builtin.sitofp_Int64_FPIEEE${bits}(zero._value)
  }

Examples:

let d = Double()
let f = Float()
let c = CGFloat()

Finally, all types which are imported from C have a default initializer in Swift that initializes all of the struct's fields to zero, as mentioned in the Xcode 6 release notes. Example (from Do I need to memset a C struct in Swift?):

let hints = addrinfo()