Workaround that can be used in WMF 5 February Preview to emulate const.

hacky_const.ps1

# don't use it, it's a workaround
class ClassWithConst
{
    [ValidateSet(100)]
    static [int] $CONST_FOO = 100
}

[ClassWithConst]::CONST_FOO
[ClassWithConst]::CONST_FOO = 10

# Output

100
Exception setting "CONST_FOO": "The argument "10" does not belong to the set "100" specified by the ValidateSet 
attribute. Supply an argument that is in the set and then try the command again."
At line:8 char:1
+ [ClassWithConst]::CONST_FOO = 10
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], SetValueInvocationException
    + FullyQualifiedErrorId : ExceptionWhenSetting