Laravel 中 foreach 和 forelse 的区别

I believe the answer to your question is that, essentially, ForElse is a ForEach loop, but with extra handling for empty array.

From the Laravel 5 docs on Blade Templates, an example illustrating both loops with the same list of Users as Input:

@foreach ($users as $user)
    <p>This is user {{ $user->id }}</p>
@endforeach

@forelse ($users as $user)
    <li>{{ $user->name }}</li>
@empty
    <p>No users</p>
@endforelse

现在，如果我们将其与Laravel框架的源代码进行比较，看看循环是如何编译的(当PHP在网页上呈现时，所有Blade struct 都被编译成HTML):

   /**
     * Compile the for-each statements into valid PHP.
     *
     * @param  string  $expression
     * @return string
     */
    protected function compileForeach($expression)
    {
        preg_match('/\( *(.*) +as *(.*)\)$/is', $expression, $matches);

        $iteratee = trim($matches[1]);

        $iteration = trim($matches[2]);

        $initLoop = "\$__currentLoopData = {$iteratee}; \$__env->addLoop(\$__currentLoopData);";

        $iterateLoop = '$__env->incrementLoopIndices(); $loop = $__env->getLastLoop();';

        return "<?php {$initLoop} foreach(\$__currentLoopData as {$iteration}): {$iterateLoop} ?>";
    }


   /**
     * Compile the for-else statements into valid PHP.
     *
     * @param  string  $expression
     * @return string
     */
    protected function compileForelse($expression)
    {
        $empty = '$__empty_'.++$this->forElseCounter;

        preg_match('/\( *(.*) +as *(.*)\)$/is', $expression, $matches);

        $iteratee = trim($matches[1]);

        $iteration = trim($matches[2]);

        $initLoop = "\$__currentLoopData = {$iteratee}; \$__env->addLoop(\$__currentLoopData);";

        $iterateLoop = '$__env->incrementLoopIndices(); $loop = $__env->getLastLoop();';

        return "<?php {$empty} = true; {$initLoop} foreach(\$__currentLoopData as {$iteration}): {$iterateLoop} {$empty} = false; ?>";
    }

Essentially, the ForElse loop has a built-in code and compile check for an empty input, in which case it optionally outputs an alternate display template for the empty input.

I would imagine you can use a ForEach loop in every case that you might use a ForElse loop, adding that you include and empty checks that ForElse might catch for you.

参考链接:

1. Blade Templates
2. Blade View Compile Functions