Why a full stop, "." and not a plus symbol, "+", for string concatenation in PHP?

Question

Why did the designers of PHP decide to use a full stop / period / "." as the string concatenation operator rather than the more usual plus symbol "+" ?

Is there any advantage to it, or any reason at all? Or did they just like to? :o)

Answer 1

I would too prefer to use a full stop instead of a plus sign because I usually associate + with mathematical equations.

For Example "this is a string " + 56 + 20

This would be very confusing for both the compiler/interpreter and the developer.

However the disadvantage to using full stop for concatenation operator is that it is just a dot on the screen and sometimes you can't see whether is it in the string or outside the string.

Answer 2

PHP's syntax is influenced by Perl, and . is the string concatenation operator in Perl.

In a weakly typed language there are advantages to having a different string concatenation and numeric addition operators: which one you use will influence which type the language coerces the variables to.

As it happens, Perl 6 will use a tilde ~ instead of a dot . for string concatenation, because . will be used for object member access. So it seems the designers of Perl now think it was a bad choice.

Perhaps, in Perl and PHP's early, non-Object-Oriented days, it seemed like as good a choice as any. Maybe the designers of both languages never envisaged them becoming strong OO languages.

As for whether PHP will one day ditch its -> member access syntax for ., who knows?

Answer 3

The use of the dot as string concatenation operator in PHP probably dates back to Perl. Remember that PHP once was nothing more than a bunch of Perl scripts.

Also it makes sense to have distinct string concatenation and addition operators, especially in weakly-typed languages. There are enough pitfalls in PHP already to shoot yourself in the foot, you don't need to add another one.

Answer 4

I guess it is so you can concatenate numbers with strings?

$i=100;
$str="hello";
$str2 = $str.$i

Since you don't declare variable types, with a + it could give a result of 100 instead of "hello100."

Answer 5

Logically + is used for numbers. While a dot is used to concatenate two sentences (strings) in a paragraph for example. Hence dot is used to concatenate strings. So it is pretty logical i believe. It is better that way...

Answer 6

This doesn't answer the question, just wanted to share something.

From PHP Manual: String Operators, someone posted this which I find rather interesting. Notice how the space plays a part in the output.

Excerpt:
If you attempt to add numbers with a concatenation operator, your result will be the result of those numbers as strings.

<?php

echo "thr"."ee";           //prints the string "three"
echo "twe" . "lve";        //prints the string "twelve"
echo 1 . 2;                //prints the string "12"
echo 1.2;                  //prints the number 1.2
echo 1+2;                  //prints the number 3

?>

Answer 7

I am not a PHP expert, but, how else do you do differentiate that last two lines?

$first  = 100;
$second = 20;
$stringresult     = $first . $second;
$arithmeticresult = $first + $second;

Answer 8

The most obvious reason would probably be that PHP inherits a lot of its syntax from Perl - and Perl uses a dot (.) for string concatenation.

But, we can delve deeper into it and figure out why this was implemented in Perl - the + operator is most commonly used for mathematical equations - it's only used for concatenation in languages in which the variable type can define the way in which the operator works (simple explanation, example is C#)

var intAddition = 1 + 2;
Console.WriteLine(intAddition); // Prints 3
var stringConcat = "1" + "2";
Console.WriteLine(stringConcat); // Prints "12"

^ As you can see, the + operator is used both for concatenation and addition in C#.

---

Perhaps the reasoning goes lower level and is due to the boolean algebra of logic gates - + means OR in logic gates, whereas . is used as the AND operator - which makes sense when it comes to string concatenation.

It makes sense to have two separate operators, one for concatenation and one for addition - it's just unfortunate that these two can be mixed up due to other languages.

Answer 9

Here is a bit of historical context.

• The PHP language started out as a set of Perl scripts.
• As such, PHP gets most of it's syntax from Perl.

• Perl, and by extension PHP, has untyped variables.

       "5"  ==   5
  "5" + 5   ==  10
  "5" . 5   ==  55
  

• To be able to tell the difference between addition and concatenation, they had to be two different operators.
• Perl copied the method access operator from C ->.
• This was before many of the more modern programming languages started to use . for method access.
• Concatenation is one of the more common operations, and should use fewer characters. According to Huffman coding.
• . was one of the few characters available for this use. The only other one that would make sense to use is ~, which is probably why that is now the Perl 6 concatenation operator.

Answer 10

+ should always be defined as a commutative operation (i.e., A+B = B+A). In the case of string concatenation, this is not the case ("foo" + "bar" != "bar" + "foo"). As such, + is not a good operator to use for the concatenation operation. Whether or not the language authors had this in mind when they used . instead (which is close to the multiplication operator, for which commutativity need not hold) remains to be seen, but it was a good decision nonetheless.

Answer 11

Douglas Crockford thinks that + for Concatenation is a Bad Idea:

JavaScript has its share of design errors, such as the overloading of + to mean both addition and concatenation with type coercion