How to use flags with ObjectScript?

Question

In C# this is allowed:

    [Flags]
    private enum PermissionType
    {
        Read = 0x0001,
        Write = 0x0002,
        Execute = 0x0004,
        All = Read | Write | Execute
    }

This allows:

private bool TestPerm(PermissionType p)
{
    if( PermissionType.Read & p) return true; // user can read    
    if( PermissionType.Write & p) return true; // user can write
    if( PermissionType.Execute & p) return true; // user can Execute
    //etc
}

It can be called like this:

Testperm( PermissionType.Read | PermissionType.Write ); 

I know there is no enum DataType in ObjectScript, but I think a regular class with properties like this should work...

Class Sample.AcknowledgeType Extends %RegisteredObject
{
    Property Read As %Integer [ InitialExpression = 1 ];
    Property Write As %Integer [ InitialExpression = 2 ];
    Property Execute As %Integer [ InitialExpression = 4 ];
    Property All As %Integer [ InitialExpression = 7 ];
}

This is as far as I got. How do I write the TestPerm method?

Answer 1

It doesn't work like that.

Each property you define on the object uses a field in memory (and on disk if it is a persistent class) for each instance. So rather than defining a property with an initial expression, you would probably define a class parameter for read, write, execute, and all.

Also, the MUMPS language that Cache Object Script is a superset of doesn't let you do bit twiddling. There is an extension to the language that does allow this - the $BIT built-in function. This gets/sets the value of a bitstring at the specified location in the string.

Therefore, you could try:

Parameter READ=1;
Parameter WRITE=2;
Parameter EXECUTE=3;

    Method TestPerm(Permissions as %String) as %Boolean
    {
        If $BIT(Permissions,..#READ) Quit 1
        If $BIT(Permissions,..#WRITE) Quit 1
        If $BIT(Permissions,..#EXECUTE) Quit 1
        Quit 0
    }

Without bitwise Boolean operators this isn't that handy. It gets worse.

You can't actually access the class parameters from outside the class without using the reflection capabilities in the %Dictionary package. That's too hard and too slow, so probably the best available choice is to expose the enumeration values with methods.

Method GetReadParameter()
{
    Quit ..#READ
}

So now it's possible to write:

Set $BIT(Permissions,MyObject.GetReadParameter())
Set $BIT(Permissions,MyObject.GetWriteParameter())
Set HasPermission=MyObject.TestPerm(Permissions)

So, once we're done admiring the beauty of that code, it's probably time to admit that without native bitwise Boolean operators this C# idiom just isn't worth it. Instead just make a Permissions class, with Boolean properties Read,Write, and Execute. "All" can be a computed property.

If you really want you can make a Permissions class that has Read, Write, Execute, and All, each of which is Boolean and computed. You can write getter and setter methods that access a private property and use $BIT to set and read the value. But your Boolean logic would happen with the returned values, so rather than

Testperm( PermissionType.Read | PermissionType.Write ); 

you would do

If (myPermissions.Read || myPermissions.Write)