array_reduce() can't work as associative-array "reducer" for PHP?

Question

I have an associative array $assoc, and need to reduce to it to a string, in this context

$OUT = "<row"; foreach($assoc as $k=>$v) $OUT.= " $k=\"$v\""; $OUT.= '/>'; 

How to do in an elegant way the same thing, but using array_reduce()

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Near the same algorithm (lower performance and lower legibility) with array_walk() function,

 array_walk(  $row, function(&$v,$k){$v=" $k=\"$v\"";}  );  $OUT.= "\n\t<row". join('',array_values($row)) ."/>"; 

Ugly solution with array_map() (and again join() as reducer):

  $row2 = array_map(      function($a,$b){return array(" $a=\"$b\"",1);},     array_keys($row),     array_values($row)   ); // or     $OUT ="<row ". join('',array_column($row2,0)) ."/>"; 

PS: apparently PHP's array_reduce() not support associative arrays (why??).

Answer 1

First, array_reduce() works with associative arrays, but you don't have any chance to access the key in the callback function, only the value.

You could use the use keyword to access the $result by reference in the closure like in the following example with array_walk(). This would be very similar to array_reduce():

$array = array(     'foo' => 'bar',     'hello' => 'world' );  // Inject reference to `$result` into closure scope. // $result will get initialized on its first usage. array_walk($array, function($val, $key) use(&$result) {     $result .= " $key=\"$val\""; }); echo "<row$result />"; 

Btw, imo your original foreach solution looks elegant too. Also there will be no significant performance issues as long as the array stays at small to medium size.