连接命名空间类静态变量的最佳方法是什么？

Question

In PHP we can do things like this:

$who = 'world';
$a = 'hello ' . $who;

or

$a = "hello $who";

or

$a = "hello {$who}"

Quoting Stephen Clay from php.net into the String operators section the last way is the best because when we use dots PHP is forced to re-concatenate all string. Also if we need to concat more variables, the last is a better way than the second way. But, Which is the best way if I have to concat a value from a class static variable ? PHP throws error if you try to concat the variable directly into a namespace class, without using dots. Only the first way shown before is allowed. I want to know if there is some another way to do this

ERROR:

$a = "hello 
amespace\classname::$who"; //NOTICE: undefined variable who
$b = "hello ${
amespace\classname::$who}"; //NOTICE: undefind variable classname
$c = "hello 
amespace\classname::${who}"; //NOTICE: undefine variable who.
$d = "hello {
amespace\classname::$who}"; //NOTICE: undefine variable who

I tried to explain with simple code, the really is that I need to concat a static variable from a class who I can't get an instance. If you get some class into a variable and later try to concat the static property this run correctly also

$who = new 
amespace\classname();
$a = "{$who::$who} $a"; // this run ok.

Answer 1

The problem with something like...

$d = "hello {
amespace\classname::$who}"

is that the {} would normally expect just a variable to do a substitution, but as it sees amespace\classname is wouldn't know if this was a literal piece of text or not, so it defaults to being a literal and then gets to $who and so looks for a variable in the current namespace.

If you can't get an instance of the class, you can still set a variable with the name of the class...

$class = namespace\classname::class;
echo "Hello {$class::$who}";