Scala future, Sing#

[Andrei Alexandrescu]

Walter Bright wrote:
>>>> Especially the array literal type inference is really naive.
>>> How should it be done?
>>
>> You shouldn't use the type of the first given element when 
>> constructing the type of the array. If you have [ e_1, ..., e_n ], the 
>> type of the literal is
>> unify(type_of_e_1, ..., type_of_e_n) + "[]". For instance:
>>
>> => typeof([ [], [1,2,3] ])
>> => unify( typeof([]), typeof([1,2,3]) ) + "[]"
>> => unify( "a[]", unify(typeof(1),typeof(2),typeof(3)) + "[]" ) + "[]"
>> => unify( "a[]", unify("int","int","int") + "[]" ) + "[]"
>> => unify( "a[]", "int" + "[]" ) + "[]"
>> => unify( "a[]", "int[]" ) + "[]"   // a is a local type var, subst = 
>> { a -> int }
>> => "int[]" + "[]"
>> => "int[][]"
> 
> Ok.

Walter: I told you :o).

I'd already defined the unify meta-function, it's called CommonType, see

http://www.digitalmars.com/d/2.0/phobos/std_traits.html#CommonType

You pass any number of types and it will figure out the type that all 
types can be converted to. Using that, it is trivial to define functions 
that infer array types properly. At a point I had an array() function 
that took any number of arguments and returned a correctly-typed array. 
Then I dropped that and defined array() in std with a different meaning 
(transform a range into an array).


Andrei