Integer promotion... what I'm missing? (It's monday...)

[Daniel Keep]

Paolo Invernizzi wrote:
> Hi all,
> 
> What I'm missing?
> 
>     uint a = 16;
>     int b = -1;
>     assert( b < a ); // this fails! I was expecting that -1 < 16
> 
> Thanks
> 
> ---
> Paolo

If you read http://digitalmars.com/d/type.html, you will find the rules
for integer promotion under arithmetic operations (which I assume also
includes comparisons).

Note point 5.4 under "Usual Arithmetic Conversions":

5.4. The signed type is converted to the unsigned type.

Hence, b is being converted to a uint.  cast(uint)(-1) = ~0 = uint.max,
hence why b is not less than a.

If you're going to compare a signed and unsigned type directly, it's
best to explicitly cast them to a common type, or strange things like
this could happen :)  Either convert a to an int (and watch for
overflow), or convert them both to a long (so you don't have problems
with overflow).

	-- Daniel

-- 
Unlike Knuth, I have neither proven or tried the above; it may not even
make sense.

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