Note, with "is" or an intrinsic that only does a range check, it can be
made very fast when platform-specific. For example, for "Result :=
(Value is TMyEnum);", under x86, if "l" is the Low value and "h" is the
High value, then the assembly becomes this (remember that l and h are
constants, so h - l is also constant and determined at compile time):
MOV REG, Value
SUB REG, l
CMP REG, (h - l)
SETNA Result
If l = 0, which is very common for most enumerations, then the assembly
is even simpler, not requiring a temporary register:
CMP Value, h
SETNA Result
For "If (Value is TMyEnum) then", the SETNA instruction becomes a
conditional jump.
In this instance, the intrinsic's function is similar to how "Inc(X);"
is a shorthand for "X := X + 1;", there for convenience more than
anything but traditionally able to produce more optimal code.
Gareth aka. Kit
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