typeof and block statements

[simendsjo]

On 12.08.2010 15:30, Steven Schveighoffer wrote:
> On Thu, 12 Aug 2010 09:13:54 -0400, simendsjo
> <simen.endsjo at pandavre.com> wrote:
>
>> The spec doesn't mention anything about block statements in typeof
>> declarations.
>>
>> //typeof({1}) a; // found } expecting ;
>> //typeof({1}()) b; // same as a
>> typeof(1) c; // int
>
> {...} is a function literal, a lambda function if you will.

I thought parameterless delegates were written () {}..

> Your lambda function contains a syntax error, the single line in it does
> not end in a semicolon.
>
> Of course, if you made it:
>
> {1;}
>
> I think it might fail anyways, because 1; is not a statement.

Why doesn't this work then?
typeof({return 1;}()) a; // found 'a' when expecting ';' following statement

>>
>> I'm asking because isInputRange from std.range the idom from the b test:
>>
>> template isInputRange(R)
>> {
>> enum bool isInputRange = is(typeof(
>> {
>> R r; // can define a range object
>> if (r.empty) {} // can test for empty
>> r.popFront; // can invoke next
>> auto h = r.front; // can get the front of the range
>> }()));
>> }
>
> is(typeof(...)) is sort of a hack to determine if something compiles or
> not. If it does, then there will be a type associated with the
> expression, if not, then there will be no type. There is also a
> __traits(compiles, ...) which I think really should be used for this
> purpose, but the isInputRange may predate that idiom.
>
> Essentially, the isInputRange bool is true if the function literal that
> contains those four statements compiles. What it translates to is, Does
> R support the functions necessary for input ranges.
>
> I see a syntax error there, r.popFront is not a property, so it should
> look like this:
>
> r.popFront();
>
> It only works right now because mandatory () for non-properties is not
> implemented in the compiler yet.

So once this is implemented, this template is always false?

>>
>>
>> Also... The unittest contains
>> static assert(isInputRange!(int[]));
>> static assert(isInputRange!(char[]));
>>
>> But arrays doesn't include these methods.. I don't understand a thing :(
>
> Arrays support "tacking on" extra methods to it. Essentially, for arrays
> (and arrays only), the compiler will translate this:
>
> arr.foo()
>
> to this:
>
> foo(arr)
>
> See http://www.digitalmars.com/d/2.0/arrays.html#func-as-property

Thanks!