Proposal: Automatic shallow Unqual on IFTI

[BCS]

Hello Lars,

> On Tue, 20 Jul 2010 16:19:50 +0000, dsimcha wrote:
> 
>> Bug 2594 (http://d.puremagic.com/issues/show_bug.cgi?id=2594) has
>> languished in Bugzilla for about 1.5 years and really irks me.
>> Furthermore, std.math.pow(), for example, doesn't work when passed
>> immutable values.  In other words, right now you can't do:
>> 
>> immutable uint foo = 5;
>> immutable uint bar = 2;
>> uint baz = foo ^^ bar;
>> Lots of functions in Phobos, as well as libs I've written, have
>> basically this bug, and fixing/preventing all instances of it is a
>> monumental and tedious task.
>> 
>> Therefore, I propose that implicit function template instantiation
>> automatically runs the equivalent of a shallow Unqual on its non-ref
>> arguments before determining the types.  In other words, if a
>> const/immutable object could be implicitly cast to shallow mutable,
>> it is.  For example:
>> 
>> void fun(T, U)(T arg1, U arg2) {
>> // Do stuff that assumes arg1, arg2 are shallowly mutable.
>> }
>> void main() {
>> immutable uint foo = 3;
>> immutable char[] bar = "bar";
>> // This instantiates fun with T = uint and U = // immutable(char)[],
>> NOT T = immutable uint and // U = immutable char[].
>> fun(foo, bar);
>> }
>> This would prevent a lot of nasty bugs but would be safe because
>> arguments passed by value are shallowly copied and therefore can
>> safely be made shallowly mutable, which is why implicitly casting
>> between fully const/immutable and shallowly mutable is allowed
>> already by the spec.
>> 
> ++vote
> 

vote++;
s/ITFI//g

Good idea, but think bigger. That is safe in general *runtime* code. OTOH 
I'd rather see the possibility of it only getting done on request be explored. 
Also allowing that as an implicit conversion on any copy is also safe.

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