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



--- Comment #10 from bearophile_hugs@eml.cc 2010-11-10 18:21:06 PST ---
The C# language, that has a very refined design, refuses this code, showing that it doesn't perform automatic joining of adjacent strings:


public class Test {
    public static void Main() {
        string s = "hello " "world";
    }
}


prog.cs(3,35): error CS1525: Unexpected symbol `world'
Compilation failed: 1 error(s), 0 warnings

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--- Comment #11 from bearophile_hugs@eml.cc 2010-11-12 04:24:57 PST ---
Walter agrees:

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=121830

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--- Comment #12 from bearophile_hugs@eml.cc 2010-11-12 04:32:16 PST ---
A comment from Andrei Alexandrescu:
Walter, please don't forget to tweak the associativity rules: var ~ " literal "
~ " literal " concatenates literals first.

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--- Comment #13 from bearophile_hugs@eml.cc 2010-11-13 19:19:03 PST ---
(In reply to comment #12)

A comment from Stewart Gordon:

> You mean make ~ right-associative?  I think this'll break more code than it fixes.
>
> But implementing a compiler optimisation so that var ~ ctc ~ ctc is processed as var ~ (ctc ~ ctc), _in those cases where they're equivalent_, would be sensible.
>
> ctc = compile-time constant

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--- Comment #14 from Ellery Newcomer <ellery-newcomer@utulsa.edu> 2010-11-13 19:26:18 PST ---
you don't need to mess with associativity rules, you just need to be able to handle two or three ast cases:

1. (~ str str)        ie  str ~ str
2. (~ (~ x str) str)  ie  x ~ str ~ str
3. (~ str (~ str x))  ie  str ~ (str ~ x)

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
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                 CC|                            |clugdbug@yahoo.com.au


--- Comment #15 from Don <clugdbug@yahoo.com.au> 2010-11-13 23:51:58 PST ---
(In reply to comment #14)
> you don't need to mess with associativity rules, you just need to be able to handle two or three ast cases:
> 
> 1. (~ str str)        ie  str ~ str
> 2. (~ (~ x str) str)  ie  x ~ str ~ str
> 3. (~ str (~ str x))  ie  str ~ (str ~ x)

Like this (optimize.c, line 1023):

Expression *CatExp::optimize(int result)
{   Expression *e;

    //printf("CatExp::optimize(%d) %s\n", result, toChars());
    e1 = e1->optimize(result);
    e2 = e2->optimize(result);

+    if (e1->op == TOKcat && (e2->op == TOKstring || e2->op == TOKnull)
+            && (((CatExp *)e1)->e2->op == TOKstring || ((CatExp *)e1)->e2->op
== TOKnull))
+    {
+        // Convert  (e ~ str) ~ str into  e ~ (str ~ str)
+        CatExp *ce = ((CatExp *)e1);
+        e1 = ce->e1;
+        ce->e1 = ce->e2;
+        ce->e2 = e2;
+        e2 = ce;
+    }
    e = Cat(type, e1, e2);
    if (e == EXP_CANT_INTERPRET)
        e = this;
    return e;
}

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--- Comment #16 from Don <clugdbug@yahoo.com.au> 2010-11-13 23:58:35 PST ---
Sorry, missed out a line:

    if (e1->op == TOKcat && (e2->op == TOKstring || e2->op == TOKnull)
            && (((CatExp *)e1)->e2->op == TOKstring || ((CatExp *)e1)->e2->op
== TOKnull))
    {
        // Convert  (e ~ str) ~ str into  e ~ (str ~ str)
        CatExp *ce = ((CatExp *)e1);
        e1 = ce->e1;
        ce->e1 = ce->e2;
        ce->e2 = e2;
        e2 = ce;
+        e2 = e2->optimize(result);
    }

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Stewart Gordon <smjg@iname.com> changed:

           What    |Removed                     |Added
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                 CC|                            |smjg@iname.com


--- Comment #17 from Stewart Gordon <smjg@iname.com> 2010-11-16 17:09:41 PST ---
(In reply to comment #5)
> 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.

Better watch out for cases where just adding ~ changes the behaviour.

For example, if a is a string[], then a ~ "this" "that" and a ~ "this" ~ "that" evaluate to different strings.

Not that there's any real use case for "this" "that" anyway.  And those rare use cases it does have in D can be fixed by inserting the ~, though there may be easier-to-miss cases of the above of which to be wary.

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--- Comment #18 from Stewart Gordon <smjg@iname.com> 2010-11-16 17:15:03 PST ---
(In reply to comment #17)
> For example, if a is a string[], then a ~ "this" "that" and a ~ "this" ~ "that" evaluate to different strings.

Different string arrays even.

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nfxjfg@gmail.com changed:

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                 CC|                            |nfxjfg@gmail.com


--- Comment #19 from nfxjfg@gmail.com 2010-11-16 19:01:06 PST ---
(In reply to comment #17)
> Not that there's any real use case for "this" "that" anyway.  And those rare use cases

I use automatic joining all the time for long string literals. I want them to
span multiple source lines without containing line breaks.
No, not a rarely used feature.

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