CODEWITHSUNDEEP
c#.netvb.netclassloaderstatic-constructor
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Reputation: 89643

Is there a standard way for .NET class loaders to work?

Is there a standard way for .NET class loaders to work?

Say I compile this code:

Option Strict On : Option Explicit On

Module Module1
    Sub Main()
        System.Diagnostics.Debug.WriteLine("Main")
        Dim g = C.A
    End Sub
End Module

Public Class C
    Shared Sub New()
        System.Diagnostics.Debug.WriteLine("Init C")
    End Sub
    Shared Property A As New A
End Class

Public Class A
    Shared Sub New()
        System.Diagnostics.Debug.WriteLine("Init A")
    End Sub
    Public Sub New()
        System.Diagnostics.Debug.WriteLine("A Constructor")
    End Sub
End Class

Can I guarantee the compiled code will (in all implemented platforms) have the following output?

Main
Init A
A Constructor
Init C

Upvotes: 3

Views: 300

Answers (2)

Ben Voigt
Ben Voigt

Reputation: 283684

Because you are using constructors and not inline initialization, the VB compiler does not mark the types with beforefieldinit, and the order is exactly controlled.

If, however, you wrote the following (using inline initialization):

Option Strict On : Option Explicit On

Module Module1
    Sub Main()
        System.Console.WriteLine("Main")
        Dim g = C.A
    End Sub
End Module
Public Class C
    Shared Function Narg() As A
        Dim alpha As New A
        System.Console.WriteLine("Init C")
        Return alpha
    End Function
    Shared Property A As A = Narg()
End Class
Public Class A
    Shared Sub New()
        System.Console.WriteLine("Init A")
    End Sub
    Public Sub New()
        System.Console.WriteLine("A Constructor")
    End Sub
End Class

the order would be unspecified. The same order as your original code would be allowed, but C can be initialized earlier. In fact, on my system the output is:

Init A
A Constructor
Init C
Main

The reason is that C now is marked beforefieldinit.

Gratuitous nit-picking: No, your original code is not guaranteed to have that output. On a release build it will have no output, because System.Diagnostics.Debug is conditionally called.

Upvotes: 4

Jon
Jon

Reputation: 437386

Yes, the order of calling static and instance constructors is part of the language specification. All conforming compilers should emit the same IL for this program.

Upvotes: 5

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