Question about iteger literals

[bearophile via Digitalmars-d-learn]

Uranuz:

> bool isDigit(char c) nothrow

This function is already in Phobos, it's std.ascii.isDigit.


> ushort hexValue(char c) nothrow

Better to use this signature (assuming you want a ushort result, 
despite a ubyte suffices and a uint is faster):

ushort hexValue(in char c) pure nothrow @safe @nogc


> 	else
> 		return ushort.max;

Special error values are not very safe. Consider the usage of a 
Nullable!(ubyte, ubyte.max) instead, if you can stand the little 
abstraction penalty.


> why these expressions are casted to int?

Because in C/C++/D if you perform arithmetic operations among 
types shorter than int you produce an int.


> I was thinking that result should be of char type.

In general it can't be a char.


> And it could be implicitly converted to ushort
> (because there is enough place to store result).

The precedent compiler version was wrong, and the bug has being 
fixed by the great Kenji.

If you have an expression like:

char - 'a' + 10

It means:

[0, 255] - 87

That is [-87, 168] that can't fit in the [0, 65535] range.

Currently in D the range value analysis works only on the current 
expression, so the information from the "if(c >= 'a' && c <= 
'f')" condition is ignored here.

There are discussions and even code to fix this:
http://forum.dlang.org/thread/lnrc8l$1254$1@digitalmars.com
https://github.com/lionello/dmd/compare/if-else-range
https://github.com/D-Programming-Language/dmd/pull/3679

But both Walter and Andrei have so far ignored this significant D 
improvement, so I don't know if and when it will be added.

Bye,
bearophile