The actual mapError function.
A new Expected object containing the result.
{
assert(expected(42).mapError!(e => e).value == 42);
assert(unexpected("foo").mapError!(e => 42).error == 42);
assert(unexpected("foo").mapError!(e => new Exception(e)).error.msg == "foo");
}
// remap hook
{
static struct Hook {}
auto res = expected(42).mapError!(e => e, Hook);
assert(res == 42);
static assert(is(typeof(res) == Expected!(int, string, Hook)));
auto res2 = unexpected!int("foo").mapError!(e => "bar", Hook);
assert(res2.error == "bar");
static assert(is(typeof(res2) == Expected!(int, string, Hook)));
}
Applies a function to the expected error in an Expected object.
If no error is present, the original value is passed through unchanged, and the function is not called.