isASCII

static assert(isASCII!'a');
static assert(!isASCII!'ä');

immutable ch = 'a';
static assert(isASCII!ch);

const cch = 'a';
static assert(isASCII!cch);

const wchar wch = 'a';
static assert(isASCII!wch);

const wchar wch_ = 'ä';
static assert(!isASCII!wch_);

const dchar dch = 'a';
static assert(isASCII!dch);

const dchar dch_ = 'ä';
static assert(!isASCII!dch_);