This will not compile:

  alias blah = null;

The dmd message are:

di/test_hdr.d(10): Error: basic type expected, not null
di/test_hdr.d(10): Error: semicolon expected to close alias declaration
di/test_hdr.d(10): Error: Declaration expected, not 'null'

Are there any other objects that cannot be aliased?

Thanks,

Best,

-Tom

On 06/12/2014 01:26 PM, Tom Browder via Digitalmars-d-learn wrote:

> This will not compile:
>
>    alias blah = null;
>
> The dmd message are:
>
> di/test_hdr.d(10): Error: basic type expected, not null
> di/test_hdr.d(10): Error: semicolon expected to close alias declaration
> di/test_hdr.d(10): Error: Declaration expected, not 'null'
>
> Are there any other objects that cannot be aliased?

alias works only with types. Being an expression (not an object), null cannot not work with alias.

Ali

On 6/12/14, 4:29 PM, Ali Çehreli wrote:
> On 06/12/2014 01:26 PM, Tom Browder via Digitalmars-d-learn wrote:
>
>  > This will not compile:
>  >
>  >    alias blah = null;
>  >
>  > The dmd message are:
>  >
>  > di/test_hdr.d(10): Error: basic type expected, not null
>  > di/test_hdr.d(10): Error: semicolon expected to close alias declaration
>  > di/test_hdr.d(10): Error: Declaration expected, not 'null'
>  >
>  > Are there any other objects that cannot be aliased?
>
> alias works only with types. Being an expression (not an object), null
> cannot not work with alias.
>
> Ali
>

void foo() {}
alias bar = foo();

Am I just misunderstanding what is meant by types?

On 06/12/2014 01:36 PM, Andrew Edwards wrote:

> void foo() {}
> alias bar = foo();
>
> Am I just misunderstanding what is meant by types?

Seems to be an old behavior. That does not compile with 2.066:

Error: function declaration without return type. (Note that constructors are always named 'this')

The following compiles though:

alias bar = foo;

I stand corrected: alias works not only with types but with symbols as well. I was right about the original code though: "Aliases cannot be used for expressions".

Ali

since null is a value maybe you want

enum blah = null;

you may also give it a type after the enum word

On Thu, Jun 12, 2014 at 4:58 PM, Adam D. Ruppe via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> wrote:
> since null is a value maybe you want
>
> enum blah = null;

That works.

> you may also give it a type after the enum word

But I can't get any other variant to work so far.

-Tom

On Thursday, 12 June 2014 at 21:58:32 UTC, Adam D. Ruppe wrote:
> since null is a value maybe you want
>
> enum blah = null;
>
> you may also give it a type after the enum word

I *think* the issue might be that "null" is an rvalue? Because you can alias variable names all you want. I do it all the time for templates where I *may* need a temporary.

eg:

void foo(T)(T val)
{
    static if (isUnsigned!T)
        alias uval = val;
    else
        auto uval = unsigned(val);
    ...
}

It's also quite useful with varargs:
alias a0 = args[0];

Also, you can't alias things like "int.init" either. I'm not sure the "rvalue" thing is the source, because these work:

//----struct S
{
    static int i;
    static int j() @property;
}
alias a = S.i;
alias b = S.j;
//----

I'd consider filling a bug report.