[Issue 4734] immutable return type specifier without parantheses confuses the compiler

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4734


Jonathan M Davis <jmdavisProg at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |jmdavisProg at gmail.com


--- Comment #1 from Jonathan M Davis <jmdavisProg at gmail.com> 2010-08-26 14:44:23 PDT ---
Unfortunately, this is not a bug. Putting either const or immutable on a
function - be it on the left of the function signature or the right - makes
that function immutable. If you want the return type to be const or immutable,
you _must_ use parens. As I understand it, this was done to make const and
immutable work the sames as modifiers like private, public, pure, and nothrow
(which mean the same thing regardless of which side of the function that
they're on). A number of use would like const and immutable to have to be on
the right if you want to make the function const or immutable, but Walter
doesn't agree, so it doesn't work that way.

So, your function declaration is making the function immutable, _not_ the
return type. The reason why using const with your unit test works but immutable
does not is because both mutable and immutable values can be used with const
functions, but only immutable ones can be used with immutable functions.

immutable test = new Test;
test.foo();

should work just fine with the way that you declared the function. Now, I think
that the error message definitely needs some work; it should indicate that the
variable needs to be immutable rather than talking about the function arguments
(it's probably doing that because the this pointer is an invisible function
argument), but it is essentially correct.

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