Type inference and overloaded functions

[Kenji Hara]

On Tuesday, 10 December 2013 at 07:15:43 UTC, Jonathan M Davis 
wrote:
> On Monday, December 09, 2013 22:59:49 Ali Çehreli wrote:
>> On 12/09/2013 10:52 PM, Jonathan M Davis wrote:
>> > On Tuesday, December 10, 2013 07:47:38 FreeSlave wrote:
>> >> I just found weird D behavior about inference of array 
>> >> types.
>> >> 
>> >> Let's suppose we have these overloaded functions:
>> >> 
>> >> import std.stdio;
>> >> 
>> >> void bar(const(int[3]) arr)
>> >> {
>> >> 
>> >>       writeln("static array");
>> >> 
>> >> }
>> >> 
>> >> void bar(const(int[]) arr)
>> >> {
>> >> 
>> >>       writeln("array slice");
>> >> 
>> >> }
>> >> 
>> >> // In main we have something like that:
>> >> int main(string[] args)
>> >> {
>> >> 
>> >>       bar([1,2,3]);
>> >>       writeln(typeof([1,2,3]).stringof);
>> >>       return 0;
>> >> 
>> >> }
>> >> 
>> >> Weird thing is that the static array version of bar is 
>> >> called,
>> >> but typeof().stringof is int[], not int[3].
>> > 
>> > Array literals are always dynamic arrays. int[3] is a static 
>> > array.
>> > 
>> > - Jonathan M Davis
>> 
>> The original question is valid then: [1,2,3] goes to the 
>> static array
>> overload.
>
> Then AFAIK, that's a bug. The type of array literals is always 
> a dynamic
> array, so they should match dynamic array overloads rather than 
> static array
> overloads, or if they match both due to an implicit conversion, 
> there should
> be an ambiguity error. Choosing the static array overload over 
> the dynamic one
> is just plain wrong.

This is an intended behavior. An array literal has dynamic array 
type *by default*.
But all of literals in D behave as polymorphic.

char c = 'A';   // character literal has char type by default
dchar d = 'A';  // but it may be implicitly typed as wchar/dchar

string str = "hello";
dstring dstr = "hello";  // string literal is implicitly typed as 
dstring

int[] darr = [1,2,3];
int[3] darr = [1,2,3];   // implicitly typed as int[3]

So, an array literal [1,2,3] is implicitly convertible both to 
int[] and int[3].
And, int[3] is more specialized than int[], so overload 
resolution will choose the first 'bar'.

Kenji Hara