Examples of Singing: "Turn On The Lights," "Loveeeeeee Song"
The fact that Future was featured on so many songs last year is a testament to the appeal of his siren-like singing voice. Needless to say, his utilization of Auto-Tune for both singing and rapping has really worked in his favor. "Turn On The Lights" poured out of every car all summer long, and since then, Future has even the most swollen of hip-hop heads considering a more sensitive definition of rap.
Conclusion: Even straight rap songs like "Same Damn Time" and "Itchin'" are manifestos of melody. Future can't avoid harmony no matter how hard the track is.