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digitalmars.D.bugs - max(byte, byte)

reply bug d.com writes:
Is this a bug?

----------------------------------------------------------------
$ cat max.d
import std.math2;

int main()
{
byte a, b;
return max(a,b);
}

----------------------------------------------------------------
$ dmd max.d
max.d(6): function std.math2.max called with argument types:
(byte,byte)
matches both:
std.math2.max(int,int)
and:
std.math2.max(real,real)

----------------------------------------------------------------

There's no partial ordering on type? e.g byte < short < int < real, so the
nearest one should be picked up?

BTW, the implementation in src/phobos/std/math2.d
is ugly:

int max(int a, int b) ...
long max(long a, long b) ...
real max(real a, real b) ...

Why can't D's template be use here?
Mar 26 2005
parent pragma <pragma_member pathlink.com> writes:
In article <d25ana$163u$1 digitaldaemon.com>, bug d.com says...
Is this a bug?

----------------------------------------------------------------
$ cat max.d
import std.math2;

int main()
{
byte a, b;
return max(a,b);
}

----------------------------------------------------------------
$ dmd max.d
max.d(6): function std.math2.max called with argument types:
(byte,byte)
matches both:
std.math2.max(int,int)
and:
std.math2.max(real,real)

----------------------------------------------------------------

There's no partial ordering on type? e.g byte < short < int < real, so the
nearest one should be picked up?

BTW, the implementation in src/phobos/std/math2.d
is ugly:

int max(int a, int b) ...
long max(long a, long b) ...
real max(real a, real b) ...

Why can't D's template be use here?

D's type-matching for function signatures is dead-simple. Either it finds an exact match, or it matches any (and all) methods with a valid implicit cast to the parameter type. In this case, byte can be implicitly cast to int *or* real, so it's complaining that your code is ambiguous. You wouldn't want to have some implicit cast ordering to resolve these matters, as that would lead to hard to debug code; in your example above, how would you know which max() function is being called?. IMO, we all want fewer such rules, rather than more. Anyway, the solution here is simple: use a shim function to remove the ambiguity.
 byte max(byte a, byte b){ return cast(byte)max(cast(int)a,cast(int)b); }

.. or use the casts directly in your code. - EricAnderton at yahoo
Mar 28 2005