Flags_Enum_Operators.md

Flags Enum Operators

Synopsis

Implement a set of immutable operations that operator over <Flags>Enums.

Dim newFlags = theseFlags!Black   ' Is all the flags set of (theseFlags) that corrispond to the set flags in (named flag: Black) set to true?
Dim newFlags = theseFlags!+Black  ' Set the flags of (theseFlags) that corrispond to the set flags in (named flag: Black) to true. 
Dim newFlags = theseFlafs!-Black  ' Clear the flag of (theseFlag) that corrispond to the set flags in (named flag: Black) to false.
Dim newFlags = theseFlags!?Black  ' Is any of the flags set in (named flag: Black) set to true.

The above set of operator also have an overload the that takes an expression.

Dim newFlags = theseFlags! (expression)
Dim newFlags = theseFlags!+(epxression)
Dim newFlags = theseFlafs!-(expression)
Dim newFlags = theseFlags!?(expression)

---

Using the flagname expr op flagname

This allow the compiler to perform addition checks at compile-time.

• are they the same enum type.
• does the named flag exist?
• Constant-Folding for better

Using expression expr op (expr)

Using this form only permits checking that they are of the same type of enum.

Implementation

The operators would corrispond the as using the method body of the following method. (Note: not calling, to allow the compiler on constant-fold)

Function IsAllSet(Of T As <Flags>Enum)( sourceFlags As T, theseFlags As T) as Boolean
  Return (sourceFlags And theseFlags) = theseFlags
End Function
Function IsAnySet(Of T As <Flags>Enum)( sourceFlags As T, theseFlags As T) As Boolean
  Return (sourceFlags And theseFlags) <> 0
End Function
Function SetFlags(Of T As <Flags>Enum)( sourceFlags As T, theseFlags As T) As T
  Return (sourcFlags Or theseFlags)
End Function
Functon ClearFlags(Of T As <Flags>Enum)( sourceFlags As T, theseFlags As T) As T
  Return (sourceFlags And (Not theseFlags))
End Function