func (g *mutableDirected) OutDegreeOf(vertex Vertex) (degree int, exists bool) {
	g.mu.RLock()
	defer g.mu.RUnlock()
	if exists = g.hasVertex(vertex); exists {
		degree = len(g.list[vertex])
	}
	return
}
/* mutableDirected additions
Returns the outdegree of the provided vertex. If the vertex is not present in the
graph, the second return value will be false.
package al
import (
	. "github.com/sdboyer/gogl"
)
type mutableDirected struct {
	al_basic_mut
}