Is it true that for all .NET operator overload methods must be public and static? - operator-overloading

Question

Quoted from C# From CLR
The CLR specification mandates that operator overload methods be
public and static methods.
I checked ECMA-335, but couldn't find any evidence.
So far I know it is true for C# and F#. Is it true for all CLS-compliant language?

Answer 1

It looks like it's not really required to be public, but making it non-static is problematic at execution time. I experimented by starting with this code:
using System;
class Oddity
{
public static Oddity operator+(Oddity x, Oddity y)
{
Console.WriteLine("Adding oddities");
return null;
}
}
class Test
{
static void Main()
{
var x = new Oddity();
var y = new Oddity();
var z = x + y;
}
}
... and then running it through ildasm, changing things, then using ilasm and running the result.
Changing the accessibility modifier to assembly (equivalent to internal): all was fine
Changing the accessibility modifier to private: it assembled (which surprised me) but then failed at execution time:
Unhandled Exception: System.MethodAccessException: Attempt by method 'Test.Main()' to access method 'Oddity.op_Addition(Oddity, Oddity)' failed.
at Test.Main()
Removing the static part: it assembled (again, surprising me) but then failed at execution time:
Unhandled Exception: System.MissingMethodException: Method not found: 'Oddity Oddity.op_Addition(Oddity, Oddity)'.
at Test.Main()
I suspect these really should be caught at assembly time, but as languages are only expected to produce operators which are public and static, the validator is a little lax.