Why is int implicitly convertible to ulong?

[Ali Çehreli]

On 02/21/2014 04:41 AM, Hannes Steffenhagen wrote:
> The specific problem here was when working with std.json.
>
> std.json distinguishes between UINTEGER and INTEGER, so I had code like
>
> static if(is(T : ulong)) {
>      // must be UINTEGER
> } else static if(is(T : long)) {
>      // can be either INTEGER or UINTEGER
> }
>
>
> I've since found out about isSigned and isUnsigned, still it was mighty
> confusing for me that the first case was selected for signed types.

I have something like the following in an experimental std.json code 
that converts to JSONValue.

Since std.json uses long for the value, I attempt to detect data loss 
when the value is a large ulong:

JSONValue to(Target : JSONValue, T)(T value)
{
/* ... */

     } else static if (is (T : long)) {
         static if (is (T == ulong)) {
             enforce(value <= long.max,
                     format("Data loss: %s %s cannot fit a long.",
                            T.stringof, value));
         }

         json.type = JSON_TYPE.INTEGER;
         json.integer = value;

     } else static if (is (T : real)) {

Ali