Re: Statically forbid string ~ size_t ?

[Steven Schveighoffer]

On Thu, 13 Oct 2011 18:34:35 -0400, Don <nos...@nospam.com> wrote:

On 13.10.2011 23:07, bearophile wrote:

This comes from a thread in D.learn.

This is a small Python2 program:


from sys import argv
x = len(argv)
s = "hello"
s += x
print s

Python is strongly typed so it refuses to append an integer number to a string:

Traceback (most recent call last):
   File "...\test.py", line 4, in<module>
     s += x
TypeError: cannot concatenate 'str' and 'int' objects

In Java if you append an integer number to a string the integer number gets first converted to a string:

class Main {
     public static void main(String[] args) {
         int x = args.length;
         String s = "hello";
         s += x;
         System.out.println(s);
     }
}


That Java code outputs:

hello0

Both Java and Python are far more commonly known than D, and they shape programmers expectations a bit.

This D2 code compiles and runs with DMD 2.056head:


void main(string[] args) {
     int x = args.length;
     string s = "hello";
     s ~= x;
}



(In this case Python2 is typed more strongly than D.)

I think that int+char is acceptable in D, but string~size_t is not good. I think this is bug prone (especially given the expectations of programmers coming from other languages). So I suggest to statically disallow string~size_t. string~char, string~dchar, and string~string are of course OK.

So far I have written no enhancement request/bug report on this because I am not so sure...

The problem is things like:
int i;
string s = "0x" ~ ('0' + x);
since char + int --> int.

string s = "0x" ~ cast(char)('0' + x);

Problem solved.

-Steve