structure制約は値型を指定してます。
構文
structure制約
Public Class クラス名(Of t As Structure)
End Class
ソース
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim s As New structureclass(Of structure1)
End Sub
End Class
Public Class structureclass(Of t As Structure)
End Class
Public Structure structure1
End Structure