http://d.puremagic.com/issues/show_bug.cgi?id=3827

           Summary: automatic joining of adjacent strings is bad
           Product: D
           Version: 2.040
          Platform: All
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-02-18 12:40:31 PST ---
import std.stdio;
void main() {
    string[] a = ["foo", "bar" "baz", "spam"];
    writeln(a);
}

This code prints:
foo barbaz spam

But probably the programmer meant to create an array with 4 strings.
D has the ~ concat operator, so to prevent possible programming bugs it's
better to remove the implicit concat of strings separated by whitespace.

Everywhere the programmer wants to concat strings the explicit concat operator can be used:

string s = "this is a very long string that doesn't fit in" ~
           " a line";

The "Python Zen" has a rule that says:

Explicit is better than implicit.

The compiler can optimize the concat away at compile time.

C code ported to D that doesn't put a ~ just raises a compile time error that's easy to understand and fix.

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--- Comment #1 from Alexey Ivanov <aifgi90@gmail.com> 2010-02-18 14:35:32 PST ---
Created an attachment (id=571)
patch for parse.c

Vote++ and patch

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--- Comment #2 from bearophile_hugs@eml.cc 2010-02-18 14:55:40 PST ---
(In reply to comment #1)
> Created an attachment (id=571) [details]
> patch for parse.c
> 
> Vote++ and patch

Thank you. But is DMD doing the joining with ~ at compile time? If not, then you can add that optimization to your patch (if you are able to).

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--- Comment #3 from bearophile_hugs@eml.cc 2010-02-18 15:03:33 PST ---
> Thank you. But is DMD doing the joining with ~ at compile time? If not, then you can add that optimization to your patch (if you are able to).

And if you think it's needed, you can add the clear error message I was talking about :-)

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Alexey Ivanov <aifgi90@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aifgi90@gmail.com


--- Comment #4 from Alexey Ivanov <aifgi90@gmail.com> 2010-02-28 09:36:58 PST ---
> Thank you. But is DMD doing the joining with ~ at compile time? If not, then you can add that optimization to your patch (if you are able to).

I think DMD is doing joining at compile time (constfold.c, from line 1387)

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--- Comment #5 from bearophile_hugs@eml.cc 2010-06-20 16:19:15 PDT ---
The error message for the missing ~ can be something like this (adapted from the "'l' suffix is deprecated, use 'L' instead" error message generated by the usage of a 10l long literal):

adjacent string literals concatenation is deprecated, add ~ between them instead.

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Ellery Newcomer <ellery-newcomer@utulsa.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ellery-newcomer@utulsa.edu


--- Comment #6 from Ellery Newcomer <ellery-newcomer@utulsa.edu> 2010-06-20 16:29:07 PDT ---
(In reply to comment #0)
> The "Python Zen" has a rule that says:
> 
> Explicit is better than implicit.
> 

the python compiler has a rule that says do the exact same thing as what d is doing.

Your serve.

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--- Comment #7 from bearophile_hugs@eml.cc 2010-06-20 16:51:06 PDT ---
I know Python, but I hope D will become better than Python on this syntax detail.

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--- Comment #8 from bearophile_hugs@eml.cc 2010-08-21 13:38:59 PDT ---
A particularly nice example of why untidy syntax easily leads to bugs (this comes from two different sources of sloppiness of the D2 language):


enum string[5] data = ["green", "magenta", "blue" "red", "yellow"];
static assert(data[4] == "yellow"); // asserts
void main() {}

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--- Comment #9 from bearophile_hugs@eml.cc 2010-11-10 18:17:17 PST ---
Another bug caused in my code by that anti-feature:


unittest {
    auto tests = [["", "0000"], ["12346", "0000"], ["he", "H000"],
                  ["soundex", "S532"], ["example", "E251"],
                  ["ciondecks", "C532"], ["ekzampul", "E251"],
                  ["resume", "R250"], ["Robert", "R163"],
                  ["Rupert", "R163"], ["Rubin" "R150"],
                  ["Ashcraft", "A226"], ["Ashcroft", "A226"]];
    foreach (pair; tests)
        assert(processit(pair[0]) == pair[1]);
}


That code compiles with no errors with DMD 2.050, and then causes a Range violation at runtime because one of those arrays isn't a pair.

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