Retrieve the specification used to build a gf_* function

Every function created by layer_factory() records the arguments (geom, stat, position, aes_form, extras, pre, aesthetics, inherit.aes, check.aes, required_packages, installed_packages) it was built with. ggformula_spec() retrieves that record, which is the recommended way for extension packages (or ggformula itself, e.g. when building _interactive counterparts) to introspect a gf_* function without depending on the internals of layer_factory().

Usage

ggformula_spec(gf_fun)

Arguments

gf_fun

A function created by layer_factory() (e.g. gf_point).

Value

A list with components geom, stat, position, aes_form, extras, pre, aesthetics, inherit.aes, check.aes, required_packages, and installed_packages, or NULL if gf_fun was not created by layer_factory().

Details

The spec is stored in the function's enclosing environment rather than as an attribute on the function, so that printing a gf_* function at the console shows just the function. Use ggformula_spec() rather than reaching for the binding directly; its name and location are an implementation detail.

Note that pre is included precisely so that interactive_layer_factory() (and similar tools) can replay it: some gf_* functions (e.g. gf_text(), whose nudge_x/nudge_y handling lives in pre, or gf_violin(), whose quantile_gp default is only valid after pre computes it) depend on pre having already run before any of their extras defaults are evaluated. Building a variant without replaying pre can therefore produce broken or even self-referential defaults.