A way to write type-agnostic script/function runnables

[Sebastian Gniazdowski <sgniazdowski@gmail.com>]

Hello,
I thought that I share a way of writing runnable objects in such a way
that they can be both invoked as a script and as a function. The main
contribution is a concise method of getting the directory path where
the object is located:

# Run as script? ZSH_SCRIPT is a Zsh 5.3 addition
if [[ $0 != example-script || -n $ZSH_SCRIPT ]]; then
    0=${${ZERO:-${0:#$ZSH_ARGZERO}}:-${(%):-%N}}
    0=${${(M)0##/*}:-$PWD/$0}

    # Such global variable is expected to be typeset'd -g
    # in the plugin.zsh file. Here it's restored in case
    # of the function being ran as a script
    typeset MY_PLUGIN_DIR=${0:h}
fi

The code is also available at Zplugin's repo – it is being added as an
example object when creating a plugin with the `create' subcommand:

https://github.com/zdharma/zplugin/blob/master/doc/example-script

I wonder if one could get the directory where the function is being
located directly, without the global *_DIR parameter? Without use of
the $*trace parameters (I don't trust them;).

-- 
Sebastian Gniazdowski
News: https://twitter.com/ZdharmaI
IRC: https://kiwiirc.com/client/chat.freenode.net:+6697/#zplugin
Blog: http://zdharma.org