[Issue 19399] Different Conversion Rules for Same Value and Type -- Enum

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19399

--- Comment #9 from Walter Bright <bugzilla at digitalmars.com> ---
(In reply to Sprink from comment #0)
> void foo(byte v) { writeln("byte ", v); }
> void foo(int v) { writeln("int ", v); }
> 
> enum A : int {
>     a = 127,
>     b = 128, // shh just ignore this
> }
> 
> void main()
> {
>     A v = A.a;
>     foo(A.a);  // byte 127
>     foo(v);    // int 127 should be byte 127
> }

foo(A.a) is passing an integer literal of type enum and value 127. 127 can be
implicitly converted to both byte and int, so foo(byte) and foo(int) both match
with conversion level 2. Partial ordering selects foo(byte).

foo(v) is passing an integer variable of type enum with a base type of int.
This cannot be implicitly converted to byte, but it can be implicitly converted
to int. Hence, foo(int) is selected. Partial ordering does not come into play.
Note that the compiler explicitly does NOT do data flow analysis in the front
end to determine that v is 127.

The compiler is working correctly as the language is designed.

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