Hypothetical concatenation predicament

问题

So I am working on a simple micro language/alternative syntax for PHP. Its syntax takes a lot from JavaScript and CoffeeScript including a few of my own concepts. I have hand written the parser (no parser generator used) in PHP to convert the code into PHP then execute it. It is more of a proof of concept/learning tool rather than anything else but I'd be lying if I said I didn't want to see it used on an actual project one day.

Anyway here is a little problem I have come across that I thought I would impose on you great intellects:

As you know in PHP the period ( . ) is used for string concatenation. However in JavaScript it is used for method chaining.

Now one thing that annoys me in PHP is having to do use that bloody arrow (->) for my method chains, so I went the JavaScript way and implemented the period (.) for use with objects.

(I think you can see the problem already)

Because I'm currently only writing a 'dumb' parser that merely does a huge search and replace, there is no way to distinguish whether a period (.) is being used for concatenation or for method chaining.

"So if you are trying to be like JavaScript, just use the addition (+) operator Franky!", I hear you scream. Well I would but because the addition (+) operator is used for math in PHP I would merely be putting myself in the same situation.

Unless I can make my parser smart enough (with a crap load of work) to know that when the addition (+) operator is working with integers then don't convert it into a period (.) for concatenation I am pretty much screwed.

But here is the cool thing. Because this is pretty much a new language. I don't have to use the period or addition operator for concatenation.

So my question is: If I was to decide to introduce a new method of string concatenation, what character would make the most sense?

回答1:

Does it have to be one character? .. could work!

Any myriad of combinations, like ~~ or >: even!

回答2:

If you don't want to use + or ., then I would recommend ^ because that's used in some other languages for string concatenation and I don't believe that it's used for anything in PHP. Edit: It's been pointed out that it's used for XOR. One option would be to use ^ anyway since bitwise XOR is not commonly used and then to map something else like ^^ to XOR. Another option would be to use .. for concatenation. The problem is that the single characters are mostly taken.

Another option would be to use +, but map it to a function which concatenates when one argument is a string and adds otherwise. In order to not break things which rely on strings which are numbers being treated as their values, we should probably treat numeric strings as numbers for these purposes. Here's the function that I would use.

function smart_add($arg1,$arg2) {
    if ($arg1.is_numeric() && $arg2.is_numeric()) {
        return $arg1 + $arg2;
    } else {
        return $arg1 . $arg2;
    }
}

Then a + b + c + d just gets turned into smart_add(smart_add(smart_add(a,b),c),d)

This may not be perfect in all cases, but it should work pretty well most of the time and has clear rules for use.

回答3:

So my question is: If I was to decide to introduce a new method of string concatenation, what character would make the most sense?

As you're well aware of, you'll need to chose a character that is not being used as one of PHP's operators. Since string concatenation is a common technique, I would try to avoid using characters that you need to press SHIFT to type, as those characters will be a hindrance.

Instead of trying to assign one character for string concatenation (as most are already in use), perhaps you should define your own syntax for string concatenation (or any other operation you need to overwrite with a different operator), as a shorthand operator (sort of). Something like:

[$string, $string]

Should be easy to pick up by a parser and form the resulting concatenated string.

Edit: I should also note that whether you're using literal strings or variables, there's no way (as far as I know) to confuse this syntax with any other PHP functionality, since the comma in the middle is invalid for array manipulations. So, all of the following would still be recognized as string concatenation and not something else in PHP.

["stack", "overflow"]
["stack", $overflow]
[$stack, $overflow]

Edit: Since this conflicts to JSON notation, the following alternative variations exist:

1. Changing the delimiter
2. Omitting the delimiter

Example:

[$stack $overflow $string $concatenation] // Use nothing (but really need space)

来源：https://stackoverflow.com/questions/8284039/hypothetical-concatenation-predicament