On Tuesday, 21 April 2015 at 19:06:39 UTC, kevin wrote:
enum bool isInputRange = is(typeof(
    (inout int = 0)
    {
        R r = R.init;     // can define a range object
        if (r.empty) {}   // can test for empty
        r.popFront();     // can invoke popFront()
        auto h = r.front; // can get the front of the range
    }));


... is the current implementation in Phobos. But I can't seem to understand this syntax. What is (inout int = 0)? Why can a block follow it?

My guess is that this is declaring some sort of function and testing if it is syntactically valid, but this is still strange to me.

It's defining a lambda function and checking that it is *semantically* valid.

No idea what the `(inout int = 0)` is there for, I would have thought it would be fine without it.

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