switch_to_post() stack implementation (similar to switch_to_blog())

[alexkingorg]

One of the challenges themes and plugins have is the balance between utilizing the core APIs that rely on global variables, while leaving things in a "clean" state for the next worker in the chain.

For example, I might have a shortcode that pulls content from another post, outputs a title or some other data, then needs to restore the previous post environment. The attached patch provides APIs for doing just this - using the same stack approach that switch_to_blog() takes in a multi-site instance.

To set up a post context, call: switch_to_post($post_id);

This can be called multiple times, diving deeper into the stack. Then each process is responsible for restoring the $post context by calling: restore_post();

This goes back to the stack, bumps out the current post and restores the previous post's context.

There is some test code for demonstration here:

​https://gist.github.com/1309915

switch_to_post implementation

This would definitely come in handy. +1

But what about in_the_loop()? Shouldn't it return false when switch_to_post() is called?

I think this is interesting. It may be better (in terms of long-term architecture) to come up with something less procedural and more object-oriented (though also much more complicated), such as WP_Post coming back from the DB and get_post()/WP_Query, thus the ability to do $post->content(), $post->title(), etc. The various template tags would then need to be reworked to rely on the current $post global. It would be similar to how is_* methods work against WP_Query.

Right, so then you wouldn't need to call switch_to_blog() at all. You could just call $whatever_post->content() directly. Relevant ticket: #12267

I'd say that as long as we have template functions for themes that rely on globals, something like this is needed.

That's just the thing. You wouldn't need to use the template tags. They would be simple wrappers for the global. Think is_single() and $wp_query->is_single().

You don't need switch_to_post() when you have access to all the posts at the same time:

$post_a = get_post( 1 );

$post_b = get_post( 2 );

$post_a->the_content();

$post_b->the_content();

But, since some of the filters on these template tags, such as 'the_content', do not pass the post id as a parameter, it's not that easy.

I agree that when WordPress has posts that are meaningful objects with proper methods, etc (as proposed in #12267) that we should be able to use those methods. For now though, I think a switch_to_post stack would be helpful.