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Enum member std.typecons.isBitFlagEnum

Detect whether an enum is of integral type and has only "flag" values (i.e. values with a bit count of exactly 1). Additionally, a zero value is allowed for compatibility with enums including a "None" value.

enum isBitFlagEnum(E) = E.min >= 0 && () { static foreach (immutable flag; EnumMembers!E) { { Base value = flag; value &= value - 1; if (value != 0) return false; } } return true; } ();

Example

enum A
{
    None,
    A = 1 << 0,
    B = 1 << 1,
    C = 1 << 2,
    D = 1 << 3,
}

static assert(isBitFlagEnum!A);

Example

Test an enum with default (consecutive) values 

enum B
{
    A,
    B,
    C,
    D // D == 3
}

static assert(!isBitFlagEnum!B);

Example

Test an enum with non-integral values 

enum C: double
{
    A = 1 << 0,
    B = 1 << 1
}

static assert(!isBitFlagEnum!C);
}

/**
A typesafe structure for storing combinations of enum values.

This template defines a simple struct to represent bitwise OR combinations of
enum values. It can be used if all the enum values are integral constants with
a bit count of at most 1, or if the `unsafe` parameter is explicitly set to
Yes.
This is much safer than using the enum itself to store
the OR combination, which can produce surprising effects like this:

enum E { A = 1 << 0, B = 1 << 1 } E e = E.A | E.B; // will throw SwitchError final switch (e) { case E.A: return; case E.B: return;

Authors

Andrei Alexandrescu, Bartosz Milewski, Don Clugston, Shin Fujishiro, Kenji Hara

License

Boost License 1.0.