[Issue 7432] DMD allows variables to be declared as pure

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=7432



--- Comment #12 from Stewart Gordon <smjg at iname.com> 2013-08-18 17:00:48 PDT ---
(In reply to comment #11)
>> In the absence of any explanation of what pure means applied to 
>> variables, I can only be assumed that pure cannot be applied to 
>> variables, and therefore any attempt to apply pure to a variable 
>> is supposed to fail with a compile error.
> 
> Except that in most cases, an invalid attribute doesn't result in a 
> compilation error - it's ignored.

You're talking about what the compiler actually does, which is a different
matter from what the spec indicates it should do.

> The argument for this is generally that it helps generic code, and 
> it makes it easier to do stuff like
> 
> attribute:
> ...
> 
> or
> 
> attribute
> {
> }
> 
> without caring about the items that it doesn't apply to.

You mean it's easier to implement if (a), (b) and (c) in the description of bug
3118 are *always* either all legal or all illegal?  To me there doesn't seem to
be much in it.

> For instance, you can do that with attributes like @safe or 
> @trusted, which have zero effect on variables and yet have lots of 
> variables declared in that code.  The same goes for pure.

Maybe.  And you could possibly argue that the criteria for purity are trivially
true for variables (since a variable cannot read or write state, or call
functions, or override, or perform I/O), but the spec speaks only of pure
_functions_.

> I don't see a good argument for
> 
> pure foo = "hello";
> 
> being legal though unless the argument is that all invalid 
> attributes are ignored (which is not the case).

Indeed, the point of pure seems to be to indicate that something is suitable
for use within a purely functional programming paradigm.  So unless we make
pure equivalent to immutable when applied to variables....

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