  Generating software from abstract models is a prime activity in
model-drivenengineering. Adaptable and extendable code generators are important
to address changing technologies as well as user needs. However, theyare less
established, as variability is often designed as configuration options of
monolithic systems. Thus, code generation is often tied to a fixed set of
features, hardly reusable in different contexts, and without means for
configuration of variants. In this paper,we present an approach for developing
product lines of template-based code generators. This approach applies concepts
from feature-oriented programming to make variability explicit and manageable.
Moreover, it relies on explicit variability regions (VR) in a code generators
templates, refinements of VRs, and the aggregation of templates and refinements
into reusable layers. Aconcrete product is defined by selecting one or multiple
layers. If necessary, additional layers required due to VR refinements are
automatically selected.
