Rollup merge of #25291 - johannhof:let-expressions-example, r=steveklabnik
Rollup merge of #25291 - johannhof:let-expressions-example, r=steveklabnik

Maybe it's me, but I really needed an example to understand if let and refutable statements.
Playpen: http://is.gd/mjX3Gf

Let me know if the variable names are too, uh, culinary.

pelmers/rust,ejjeong/rust,philyoon/rust,rohitjoshi/rust,omasanori/rust,rohitjoshi/rust,reem/rust,seanrivera/rust,carols10cents/rust,zubron/rust,mihneadb/rust,KokaKiwi/rust,ejjeong/rust,nwin/rust,vhbit/rust,aidancully/rust,zubron/rust,GBGamer/rust,dwillmer/rust,carols10cents/rust,aepsil0n/rust,jroesch/rust,philyoon/rust,zubron/rust,philyoon/rust,gifnksm/rust,aidancully/rust,aidancully/rust,l0kod/rust,krzysz00/rust,dwillmer/rust,graydon/rust,l0kod/rust,omasanori/rust,jroesch/rust,kwantam/rust,vhbit/rust,mvdnes/rust,zubron/rust,graydon/rust,XMPPwocky/rust,reem/rust,aepsil0n/rust,aneeshusa/rust,jashank/rust,vhbit/rust,l0kod/rust,carols10cents/rust,jroesch/rust,victorvde/rust,pshc/rust,aepsil0n/rust,l0kod/rust,cllns/rust,mihneadb/rust,victorvde/rust,pelmers/rust,XMPPwocky/rust,aneeshusa/rust,rohitjoshi/rust,nwin/rust,mdinger/rust,rohitjoshi/rust,TheNeikos/rust,aidancully/rust,robertg/rust,TheNeikos/rust,carols10cents/rust,pelmers/rust,mdinger/rust,graydon/rust,ejjeong/rust,zachwick/rust,aneeshusa/rust,TheNeikos/rust,krzysz00/rust,jroesch/rust,zubron/rust,jashank/rust,dwillmer/rust,robertg/rust,cllns/rust,mdinger/rust,aepsil0n/rust,jroesch/rust,ejjeong/rust,mvdnes/rust,cllns/rust,victorvde/rust,reem/rust,kwantam/rust,philyoon/rust,GBGamer/rust,vhbit/rust,jashank/rust,carols10cents/rust,gifnksm/rust,aepsil0n/rust,andars/rust,mihneadb/rust,pshc/rust,omasanori/rust,sae-bom/rust,rohitjoshi/rust,aidancully/rust,reem/rust,cllns/rust,robertg/rust,zachwick/rust,andars/rust,victorvde/rust,dwillmer/rust,jashank/rust,reem/rust,nwin/rust,gifnksm/rust,andars/rust,mdinger/rust,krzysz00/rust,kwantam/rust,XMPPwocky/rust,nwin/rust,mdinger/rust,TheNeikos/rust,pelmers/rust,seanrivera/rust,nwin/rust,KokaKiwi/rust,mihneadb/rust,TheNeikos/rust,aneeshusa/rust,jashank/rust,GBGamer/rust,l0kod/rust,vhbit/rust,mvdnes/rust,zubron/rust,mvdnes/rust,victorvde/rust,sae-bom/rust,seanrivera/rust,mvdnes/rust,dwillmer/rust,pshc/rust,aneeshusa/rust,cllns/rust,jroesch/rust,kwantam/rust,kwantam/rust,seanrivera/rust,sae-bom/rust,KokaKiwi/rust,XMPPwocky/rust,sae-bom/rust,omasanori/rust,victorvde/rust,robertg/rust,kwantam/rust,jashank/rust,pshc/rust,KokaKiwi/rust,KokaKiwi/rust,XMPPwocky/rust,dwillmer/rust,omasanori/rust,zubron/rust,krzysz00/rust,seanrivera/rust,carols10cents/rust,l0kod/rust,graydon/rust,zubron/rust,ejjeong/rust,seanrivera/rust,zachwick/rust,pelmers/rust,mvdnes/rust,mihneadb/rust,TheNeikos/rust,GBGamer/rust,nwin/rust,jashank/rust,dwillmer/rust,sae-bom/rust,ejjeong/rust,jashank/rust,jroesch/rust,pshc/rust,nwin/rust,sae-bom/rust,philyoon/rust,robertg/rust,gifnksm/rust,GBGamer/rust,mdinger/rust,l0kod/rust,pshc/rust,reem/rust,pelmers/rust,aepsil0n/rust,cllns/rust,philyoon/rust,vhbit/rust,KokaKiwi/rust,mihneadb/rust,gifnksm/rust,aidancully/rust,pshc/rust,dwillmer/rust,graydon/rust,XMPPwocky/rust,l0kod/rust,nwin/rust,robertg/rust,graydon/rust,vhbit/rust,GBGamer/rust,jroesch/rust,GBGamer/rust,andars/rust,rohitjoshi/rust,krzysz00/rust,andars/rust,krzysz00/rust,GBGamer/rust,gifnksm/rust,pshc/rust,zachwick/rust,omasanori/rust,andars/rust,zachwick/rust,aneeshusa/rust,zachwick/rust,vhbit/rust