const debacle

[Steven Schveighoffer]

"Janice Caron" wrote
> On 21/03/2008, Walter Bright wrote:
>> There's been some discussion about this, but no good resolution.
>
> Allow me to offer a suggestion.
> ...

Sorry to say this, but this idea adds nothing to templates.  Since const T, 
invariant T, and just T are all distinct types, I can just write the 
template:

T[] f(T)(T[] buf)

And it accomplishes what you are trying to do (instantiates a version based 
on the constness of T).  If I want to guarantee T is a char, I think I can 
do:

T[] f(T : char)(T[] buf)

or something similar (I don't work with D2 daily, so I'm not sure how this 
syntax would work), or if this doesn't work, use a static if.

This does not solve the problem that I had originally queried about.  The 
problem with your method is still that the non-const version does not 
guarantee that f does not change the input buffer.  I want to specify that 
the function does not change the input buffer, and returns the same type as 
passed in (without duping the input).

I have been thinking about this a lot, and I think actually in the grand 
scheme of things, this is not a blocker, as even though the compiler does 
not guarantee constness for the non-const version, one can document that a 
function is const (and even test this by compiling a const version in a 
unittest).  However, it is a hole in the const scheme, which should probably 
be fixed at some point.

-Steve