Arithmetic conversions and a surprise with 'max'

[Ali Çehreli]

The following program demonstrates a problem that I just hit. It is a 
known gotcha of arithmetic conversion rules.

The program is trying to center some text around an index of a char 
array. To avoid negative index values, it calls 'max' to limit the 
starting offset at 0.

import std.algorithm;

void main()
{
    // An empty line
    char[10] line = ' ';

    // We want to center some text around the first quarter mark
    int center_of_text = line.length / 4;
    string text = "01234567";

    // To be safe, we want to limit the starting index at 0.
    // (No negative index please!)
    int start = max(0, center_of_text - text.length / 2);

    assert(start >= 0); // FAILS!
}

The problem is due to converting the second argument of max to unsigned.

Ali