Compose catalog stats

Property definitions

nitc $ Catalog :: _catalog_stats
	# Compose catalog stats
	var catalog_stats: CatalogStats is lazy do
		var stats = new CatalogStats
		stats.packages = mpackages.length
		stats.maintainers = maint2proj.length
		stats.contributors = contrib2proj.length
		stats.tags = tag2proj.length
		stats.modules = mmodules.sum
		stats.classes = mclasses.sum
		stats.methods = mmethods.sum
		stats.loc = loc.sum
		return stats
	end
src/catalog/catalog.nit:530,2--542,4