<p>In languages like Java and C#, strings are immutable and it can be computationally expensive to build a string one character at a time.  In said languages, there are library classes to reduce this cost such as C# <code>System.Text.StringBuilder</code> and Java <code>java.lang.StringBuilder</code>.</p>

<p>Does php (4 or 5; I'm interested in both) share this limitation?  If so, are there similar solutions to the problem available?</p>

no such limitation in php,
php can concatenate strng with the dot(.) operator
```
```
$a="hello ";
$b="world";
echo $a.$b;
```
```
outputs "hello world"