On Wednesday, 17 December 2014 at 13:35:53 UTC, Marc Schütz wrote:
I think that enforcing alias-freeness by default (the way a strict linear type system requires) doesn't fit too well into the existing language. Some way of signalling this to the compiler will therefore be required. It might be as simple as C's `restrict` keyword (but it needs to be enforced!), or better yet, an `unrestrict` keyword. Parameters would be alias-free by default unless explicitly specified otherwise. Local aliases (inside one function) are however ok, as long as not more than one is passed to another function at the same time.
Hmm, I kind of feel that D is having too many parameter keywords/types/qualifiers. Parameter specification is primarily useful where it provides information about constraints that the programmer need to know about when using a library.
"restricted scope ref" could be a useful default for non-templated functions, then use templated ownership reference typing or inference to go beyond it.
I think that if one improved the templating system so that it was capable of analysing similarities between instantiations and use heuristics to analyse when a new instance is profitable then you could make functions templated by default and propagate knowledge from the call site to the template-instantiation mechanism of the compiler. So if the reference is known to be aliasfree then the compiler can use heuristics to determine if it should instantiate a "restricted" version or use a slower general version of the templated function.
Similarily, if refcounters always are on offset 0 and destructors are virtual, then you only need a single container method template instance for refcouting references, even if you have many types using the same method. If refcounters are big enough, you can have a unique_ptr that just set it to a large value and use the same template instance for a unique_ptr and refcounted_ptr behind the scene when referencing objects that provide a refcount field.
There are also many other things that could be done to enhance the template system, like querying properties of the block in loops that iterate over a "range", so that you can instantiate different "optimized ranges" depending on whether the loop contains a "break" statement or not. Or like Jonathan Blow's language, where you can issue a "remove element and continue" like statement within a foreach-loop, which might require a different "range iteration" implementation.
