require (modname)
Loads the given module. The function starts by looking into the package.loaded
table to determine whether modname
is already loaded. If it is, then require
returns the value stored at package.loaded[modname]
. Otherwise, it tries to find a loader for the module.
To find a loader, require
is guided by the package.searchers
sequence. By changing this sequence, we can change how require
looks for a module. The following explanation is based on the default configuration for package.searchers
.
First require
queries package.preload[modname]
. If it has a value, this value (which must be a function) is the loader. Otherwise require
searches for a Lua loader using the path stored in package.path
. If that also fails, it searches for a C loader using the path stored in package.cpath
. If that also fails, it tries an all-in-one loader (see package.searchers
).
Once a loader is found, require
calls the loader with two arguments: modname
and an extra value dependent on how it got the loader. (If the loader came from a file, this extra value is the file name.) If the loader returns any non-nil value, require
assigns the returned value to package.loaded[modname]
. If the loader does not return a non-nil value and has not assigned any value to package.loaded[modname]
, then require
assigns true to this entry. In any case, require
returns the final value of package.loaded[modname]
.
If there is any error loading or running the module, or if it cannot find any loader for the module, then require
raises an error.
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