@trust is an encapsulation method, not an escape

[weaselcat via Digitalmars-d]

On Friday, 6 February 2015 at 05:32:48 UTC, Walter Bright wrote:
> On 2/5/2015 9:00 PM, "Ola Fosheim =?UTF-8?B?R3LDuHN0YWQi?= 
> <ola.fosheim.grostad+dlang at gmail.com>" wrote:
>> On Thursday, 5 February 2015 at 23:39:39 UTC, Walter Bright 
>> wrote:
>>>  static void trustedMemcopy(T[] dest, T[] src) @trusted
>>>  {
>>>    assert(src.length == dest.length);
>>>    memcpy(dest.ptr, src.ptr, src.length * T.sizeof);
>>>  }
>>>
>>> I don't have to review callers of trustedMemory() because it 
>>> encapsulates an
>>> unsafe operation (memcpy) with a safe interface.
>>
>> It might have done so if it ensured that T was a proper value 
>> type, but
>> unfortunately D's type system is not strong enough.
>>
>> What happens if T is a unique_ptr style reference? Ouch, two 
>> unique references
>> to the same object. Ouch, memory unsafe.
>
> Good point. Then a constraint can be added to the function 
> signature that T is copyable.
>
> D's type system is strong enough for that.

What's the "D way" of checking if a parameter is a reftype, 
valuetype, etc?