Repository navigation
Calling base class method in a System.Xml.XmlNode-derived custom class fails; invokes own method instead, resulting in infinite recursion #6386
Description
The documented syntax for invoking a base-class method from a PS custom class is
([<base-class>] $this).<method>(), but that doesn't seem to work, as discovered in this SO question.
Instead, the derived class' method itself is invoked, resulting in infinite recursion.
Update: The problem appears to be specific to [System.Xml.XmlNode]-derived classes; see @daxian-dbw's comment below.
A reflection-based workaround can be found in this answer.
Steps to reproduce
class child : System.Xml.XmlDocument {
[void] LoadXml([string]$content) {
Write-Host 'Inside overridden LoadXml.'
# Try to call the base type's .LoadXml() method.
([System.Xml.XmlDocument] $this).LoadXml($content)
}
}
[child]::new().LoadXml('<foo>bar</foo>')Expected behavior
Inside overridden LoadXml.
The message should print once, and the XML string should be loaded into the instance via the call to the base-class method.
Actual behavior
Inside overridden LoadXml.
Inside overridden LoadXml.
...
The method keeps calling itself and eventually runs into a call-depth overflow.
Environment data
PowerShell Core v6.0.1 on macOS 10.13.3
PowerShell Core v6.0.1 on Ubuntu 16.04.3 LTS
PowerShell Core v6.0.1 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)
Windows PowerShell v5.1.15063.674 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)
Activity
BrucePay commentedon Mar 13, 2018
It seems to work, at least in simple cases, when you are extending a PowerShell class as in:
Jason Shirk (@lzybkr) Thoughts?
lzybkr commentedon Mar 13, 2018
Sorry, no idea what is going on here.
daxian-dbw commentedon Mar 14, 2018
This is not specific to powershell class. It repros with a regular type added with
Add-Type:This is actually specpfic to types that derive from
System.Xml.XmlNode. The primary adapter of such a type is theXmlNodeAdapter, which is not optimizable (SiteBinderCanOptimizereturnsfalse). In such case, the invocation is done through theInvokemethod of the adapter, instead ofPSInvokeMemberBinder.InvokeDotNetMethod, and therefore, thePSMethodInvocationConstraintsis not respected.[-]Calling base class method in a custom class fails; invokes own method instead, resulting in infinite recursion[/-][+]Calling base class method in a System.Xml.XmlNode-derived custom class fails; invokes own method instead, resulting in infinite recursion[/+]