Choosing between __traits(compiles, { ... } ) and is(typeof( { ... } ))

[Nordlöw]

On Wednesday, 20 September 2017 at 12:20:18 UTC, Stefan Koch 
wrote:
> Yes there are.
> Prefer __traits(compiles) it includes stricter visibility 
> checks then is() does.

1. Can you give example of such visibility checks?

2. If so, should `isCopyable` (along with more defs in 
std.traits) be converted to instead use `__traits(compiles, )` ?

3. And how do the two idioms differ in terms of compilation-speed?