Sometimes in a program instances of enumerates values contain a value that's not one of the allowed ones, because of missed initialization ("= void"), data corruption, badly done casts of integral values to enum instance values, and so on.

So I sometimes validate an enum instance in function pre-conditions. Below there is a first implementation of such isValidEnumValue() validating function, meant to be used mostly in pre-conditions. I suggest to add something similar to this to std.exception:


//------------------------------------------
import std.traits: EnumMembers, isIntegral, isSomeChar;
import std.algorithm: canFind;

@property bool isCompleteIntervalEnum(E)()
pure nothrow if (is(E == enum)) {
    static if (isIntegral!E || isSomeChar!E) {
        return EnumMembers!E.length == (E.max - E.min + 1);
    } else {
        return false;
    }
} unittest { // isCompleteIntervalEnum tests
    enum E01 : string { S1="abb", S2="booh", S3="zum" }
    static assert(!isCompleteIntervalEnum!E01);

    enum E02 : byte { A=-3, S2=4 }
    static assert(!isCompleteIntervalEnum!E02);

    enum E03: byte { A=0, B=1, C=2 }
    static assert(isCompleteIntervalEnum!E03);

    enum E04: char { A, B, C }
    static assert(isCompleteIntervalEnum!E04);

    enum E05: ulong { A=ulong.max, B=ulong.min }
    static assert(!isCompleteIntervalEnum!E05);

    enum E06: ulong { A=ulong.max, B=ulong.max-1 }
    static assert(isCompleteIntervalEnum!E06);

    enum E07: char { A='a', B='b', C='c' }
    static assert(isCompleteIntervalEnum!E07);
}

bool isValidEnumValue(E)(E e)
pure nothrow if (is(E == enum)) {
    static if (isCompleteIntervalEnum!E) {
        return e >= E.min && e <= E.max; // Optimization.
    } else {
        return [EnumMembers!Foo].canFind(e);
    }
}

enum Foo { A, B, C=10 }

void bar(Foo f)
in {
    assert(isValidEnumValue(f));
} body {
}

void main() {
    //Foo f;
    Foo f = void;
    bar(f);
}
//------------------------------------------