User Defined Attributes

[bearophile]

For the syntax maybe it's better something like @() instead of 
[], so it becomes more greppable and more easy to tell apart 
visually from the array literals:

@(1, "xx", Foo) int x;


Supporting annotations for function arguments is probably an 
important sub-feature.

Yesterday I was discussing about the bug-prone nature of foreach 
loops on a struct array, and one of the solutions I've suggested 
was a user-defined annotation for the programmer to denote that 
she wants to modify just the copy:

struct Foo {}
Foo[10] foos;
foreach (@copy f; foos) { ... }

With UDA syntax:

foreach ([Copy] f; foos) { ... }
Or:
foreach (@(Copy) f; foos) { ... }

But I think there's no way to tell the compiler to give a 
compile-time error if such annotation is not present there 
(unless there's "ref").

---------------------

Gor Gyolchanyan:

> @flags enum A { ... }
>
> the "flags" attribute would replace the declaraction of A with 
> another enum declaration with the same name and same members, 
> but with replaced initialization and would static assert(false, 
> "flags enum can't have initializers") if any initializers are 
> given.

I appreciate your idea (I think of user-defined attributes also 
as ways to extend the type system), But I know the engineer in 
Walter prefers extra-simple ideas, so maybe your idea will not be 
accepted :-) But let's see.

Bye,
bearophile