Add a fluent Stringable Str::of($string)->if() method to allow longer chaining of a Stringable, based on the Stringable itself

src/Illuminate/Support/Stringable.php

@@ -237,6 +237,23 @@ public function finish($cap)
         return new static(Str::finish($this->value, $cap));
     }
 
+    /**
+     * Conditionally apply a callback to the stringable, based on the stringable value itself.
+     *
+     * @param  callable  $condition
+     * @param  callable|null  $true
+     * @param  callable|null  $false
+     * @return static
+     */
+    public function if($condition, $true, $false = null)
+    {
+        if ($condition($this)) {
+            return new static($true ? $true($this) : $this);
+        } else {
+            return new static($false ? $false($this) : $this);
+        }
+    }
+
     /**
      * Determine if a given string matches a given pattern.
      *

tests/Support/SupportStringableTest.php

@@ -404,6 +404,59 @@ public function testFinish()
         $this->assertSame('abcbbc', (string) $this->stringable('abcbbcbc')->finish('bc'));
     }
 
+    public function testIf()
+    {
+        $this->assertSame('200 is numeric',
+            (string) $this->stringable(' 200')
+                ->if(function ($stringable) {
+                    return is_numeric((string) $stringable);
+                }, function ($stringable) {
+                    return $stringable->append(' is numeric');
+                }, function ($stringable) {
+                    return $stringable->append(' is not numeric');
+                })->trim());
+
+        $this->assertSame('Laravel is not numeric',
+            (string) $this->stringable(' Laravel')
+                ->if(function ($stringable) {
+                    return is_numeric((string) $stringable);
+                }, function ($stringable) {
+                    return $stringable->append(' is numeric');
+                }, function ($stringable) {
+                    return $stringable->append(' is not numeric');
+                })->trim());
+
+        $this->assertSame(
+            'It keeps a string the same if $true = null',
+            (string) $this->stringable('It keeps a string the same if $true = null ')
+                ->if(function () {
+                    return true;
+                }, null, function ($stringable) {
+                    return $stringable->replace('keeps', 'doesn\'t keep');
+                })->trim()
+        );
+
+        $this->assertSame(
+            'It keeps a string the same if $false = null',
+            (string) $this->stringable('It keeps a string the same if $false = null ')
+                ->if(function () {
+                    return false;
+                }, function ($stringable) {
+                    return $stringable->replace('keeps', 'doesn\'t keep');
+                }, null)->trim()
+        );
+
+        $this->assertSame(
+            'It keeps a string the same if $false = null and third parameter omitted',
+            (string) $this->stringable('It keeps a string the same if $false = null and third parameter omitted ')
+                ->if(function () {
+                    return false;
+                }, function ($stringable) {
+                    return $stringable->replace('keeps', 'doesn\'t keep');
+                })->trim()
+        );
+    }
+
     public function testIs()
     {
         $this->assertTrue($this->stringable('/')->is('/'));