On 7/5/2013 9:17 AM, H. S. Teoh wrote:
> Python uses +.

There's much historical precedence for + meaning concatenation, and much historical experience with the resulting ambiguity. The famous example is:

    "123" + 4

? In D, the canonical problem is:

    int[] array;

    array + 4

Does that mean append 4 to array, or add 4 to each element of array? What if you want to create a user defined type that supports both addition and concatenation?

Use + for addition, ~ for concatenation, and all these problems go away.

On Friday, 5 July 2013 at 14:59:39 UTC, TommiT wrote:
> It's rather C++'s std::string which overloads the meaning of + to mean "concatenation". I wonder if some other programming language has assigned some other symbol (than ~) to mean "concatenation". I guess math uses || for it.

|| is used for a different kind of concatenation [1]

For strings, math uses middle dot, (a⋅b) or even just (ab) like with multiplication [2]

[1]: https://en.wikipedia.org/wiki/Concatenation_(mathematics)
[2]: https://en.wikipedia.org/wiki/String_operations#Strings_and_languages

On Fri, Jul 05, 2013 at 10:44:43AM -0700, Walter Bright wrote:
> On 7/5/2013 9:17 AM, H. S. Teoh wrote:
> >Python uses +.
> 
> There's much historical precedence for + meaning concatenation, and much historical experience with the resulting ambiguity.

Which leads to some nasty situations in Javascript, where sometimes what you think is an int, is actually a string, and you wonder why your calculation is producing strange results. Or vice versa, when you're trying to concatenate strings, and get a strange large number instead.


> The famous example is:
> 
>     "123" + 4
> 
> ? In D, the canonical problem is:
> 
>     int[] array;
> 
>     array + 4
> 
> Does that mean append 4 to array, or add 4 to each element of array? What if you want to create a user defined type that supports both addition and concatenation?
> 
> Use + for addition, ~ for concatenation, and all these problems go away.

It doesn't necessarily have to be ~, as long as it's something other than + (or any other numerical binary operator). Perl uses '.', but in D's case, that would be a bad idea, since you'd have ambiguity in:

	auto x = mod1.x . mod2.y; // concatenation or long module path name?

It's not a problem in Perl, because Perl uses :: as module separator, like C++.

Your example is somewhat faulty, though; adding 4 to each element of the array would have to be written "array[] + 4", wouldn't it? You can't make the [] optional, because if you have an array of arrays, then you're in trouble:

	int[][] aoa;
	aoa ~ [1];	// append to outer array, or each inner array?

While it's possible to use type-matching to decide, it seems like a bug waiting to happen. Much better if array <op> x always means apply <op> to the entire array, and array[] <op> x to mean apply <op> to each array element.


T

-- 
People tell me I'm stubborn, but I refuse to accept it!

On Friday, July 05, 2013 16:59:38 TommiT wrote:
> On Tuesday, 2 July 2013 at 23:28:41 UTC, monarch_dodra wrote:
> > On Tuesday, 2 July 2013 at 21:48:54 UTC, Walter Bright wrote:
> >> On 7/2/2013 1:47 PM, TommiT wrote:
> >>> Division operator for strings doesn't make any sense,
> >> 
> >> That's why overloading / to do something completely unrelated to division is anti-ethical to writing understandable code.
> > 
> > s/division/"The common agreed upon semantic"/
> > 
> >> The classic example of this is the overloading of << and >> for stream operations in C++.
> > 
> > Or overloading ~ to mean "concat" ?
> 
> It's rather C++'s std::string which overloads the meaning of + to mean "concatenation". I wonder if some other programming language has assigned some other symbol (than ~) to mean "concatenation". I guess math uses || for it.

Most languages I've used use + for concatenating strings, so it was definitely surprising to me that D didn't. I have no problem with the fact that it has a specific operator for concatenation (and there are some good reasons for it), but + seems to be pretty standard across languages from what I've seen. I've certainly never seen another language use ~ for that purpose, but at the moment, I can't remember whether I've ever seen another programming language use ~ for _any_ purpose.

- Jonathan M Davis

> Most languages I've used use + for concatenating strings, so it was definitely
> surprising to me that D didn't. I have no problem with the fact that it has a
> specific operator for concatenation (and there are some good reasons for it),
> but + seems to be pretty standard across languages from what I've seen. I've
> certainly never seen another language use ~ for that purpose, but at the
> moment, I can't remember whether I've ever seen another programming language
> use ~ for _any_ purpose.
>
> - Jonathan M Davis
logical not in e.g. Java?

On 07/05/2013 09:43 PM, Namespace wrote:
>> Most languages I've used use + for concatenating strings, so it was
>> definitely
>> surprising to me that D didn't. I have no problem with the fact that
>> it has a
>> specific operator for concatenation (and there are some good reasons
>> for it),
>> but + seems to be pretty standard across languages from what I've
>> seen. I've
>> certainly never seen another language use ~ for that purpose, but at the
>> moment, I can't remember whether I've ever seen another programming
>> language
>> use ~ for _any_ purpose.
>>
>> - Jonathan M Davis
> logical not in e.g. Java?

Unary ~ is bitwise not in Java and D, and he is referring to binary usage.

> Unary ~ is bitwise not in Java and D, and he is referring to binary usage.

> [...] use ~ for _any_ purpose.
I'd expected that *any* really means *any* and do not refer to binary.

On Friday, July 05, 2013 22:09:53 Namespace wrote:
> > Unary ~ is bitwise not in Java and D, and he is referring to binary usage.
> > 
> > [...] use ~ for _any_ purpose.
> 
> I'd expected that *any* really means *any* and do not refer to binary.

I did mean any, not just binary. I thought that there might be a case of it being used as a unary operator somewhere in at least one language I'd used, but I couldn't think of any when I posted (probably due to a combination of just having gotten up and the fact that I use bitwise operations very rarely).

- Jonathan M Davis

On 07/05/2013 10:09 PM, Namespace wrote:
>> Unary ~ is bitwise not in Java and D, and he is referring to binary
>> usage.
>
>> [...] use ~ for _any_ purpose.
> I'd expected that *any* really means *any* and do not refer to binary.

Yes. Neither do 'use', 'for' and 'purpose'. Establishing that it is likely that ~ is referring to binary requires some more context (eg. it is likely that the two usages of ~ in his post refer to the same thing), common sense or the assumption that Jonathan probably knows about the unary usage. (Parsing natural language is quite hard though, so I could be wrong.)

On 07/05/2013 10:34 PM, Timon Gehr wrote:
> On 07/05/2013 10:09 PM, Namespace wrote:
>>> Unary ~ is bitwise not in Java and D, and he is referring to binary
>>> usage.
>>
>>> [...] use ~ for _any_ purpose.
>> I'd expected that *any* really means *any* and do not refer to binary.
>
> Yes. Neither do 'use', 'for' and 'purpose'. Establishing that it is
> likely that ~ is referring to binary requires some more context (eg. it
> is likely that the two usages of ~ in his post refer to the same thing),
> common sense or the assumption that Jonathan probably knows about the
> unary usage. (Parsing natural language is quite hard though, so I could
> be wrong.)
>

Turns out I was wrong. :o)