auto merge of #11567 : divtxt/rust/master, r=cmr
auto merge of #11567 : divtxt/rust/master, r=cmr

I found the boxes diagram in the tutorial misleading about how the enum worked.

The current diagram makes it seem that there is a separate Cons struct when there is only one type of struct for the  List type, and Nil is drawn almost as if it's not consuming memory.

I'm aware of the optimization that happens for this enum which takes advantage of the fact that pointer cannot be null but this is an implementation detail and not the only one that applies here.  I can add a note below the diagram mentioning this if you like.

emk/rust,philyoon/rust,AerialX/rust-rt-minimal,richo/rust,miniupnp/rust,emk/rust,hauleth/rust,aidancully/rust,AerialX/rust,servo/rust,bombless/rust-docs-chinese,TheNeikos/rust,avdi/rust,rohitjoshi/rust,jashank/rust,servo/rust,AerialX/rust,ruud-v-a/rust,seanrivera/rust,mihneadb/rust,Ryman/rust,mitsuhiko/rust,nham/rust,XMPPwocky/rust,ebfull/rust,aneeshusa/rust,stepancheg/rust-ide-rust,philyoon/rust,mdinger/rust,zaeleus/rust,michaelballantyne/rust-gpu,vhbit/rust,ruud-v-a/rust,zaeleus/rust,avdi/rust,mitsuhiko/rust,ruud-v-a/rust,barosl/rust,Ryman/rust,dinfuehr/rust,gifnksm/rust,ebfull/rust,stepancheg/rust-ide-rust,graydon/rust,philyoon/rust,aturon/rust,nwin/rust,GBGamer/rust,seanrivera/rust,rohitjoshi/rust,aneeshusa/rust,nham/rust,TheNeikos/rust,sae-bom/rust,TheNeikos/rust,rprichard/rust,ktossell/rust,gifnksm/rust,barosl/rust,rohitjoshi/rust,KokaKiwi/rust,sae-bom/rust,dwillmer/rust,jashank/rust,michaelballantyne/rust-gpu,0x73/rust,andars/rust,Ryman/rust,zachwick/rust,dwillmer/rust,dwillmer/rust,Ryman/rust,mitsuhiko/rust,zachwick/rust,ktossell/rust,P1start/rust,robertg/rust,miniupnp/rust,TheNeikos/rust,carols10cents/rust,victorvde/rust,zaeleus/rust,vhbit/rust,cllns/rust,hauleth/rust,victorvde/rust,P1start/rust,emk/rust,vhbit/rust,servo/rust,sae-bom/rust,erickt/rust,pshc/rust,pythonesque/rust,defuz/rust,zaeleus/rust,mvdnes/rust,dwillmer/rust,zubron/rust,rprichard/rust,cllns/rust,huonw/rand,P1start/rust,mitsuhiko/rust,bombless/rust,carols10cents/rust,quornian/rust,dwillmer/rust,seanrivera/rust,vhbit/rust,mahkoh/rust,vhbit/rust,ebfull/rust,michaelballantyne/rust-gpu,carols10cents/rust,aneeshusa/rust,zubron/rust,GBGamer/rust,barosl/rust,l0kod/rust,AerialX/rust-rt-minimal,bhickey/rand,nwin/rust,Ryman/rust,krzysz00/rust,ejjeong/rust,kimroen/rust,reem/rust,aepsil0n/rust,cllns/rust,sae-bom/rust,quornian/rust,michaelballantyne/rust-gpu,erickt/rust,graydon/rust,KokaKiwi/rust,ktossell/rust,aturon/rust,shepmaster/rand,miniupnp/rust,ejjeong/rust,servo/rust,reem/rust,GBGamer/rust,quornian/rust,pelmers/rust,aneeshusa/rust,bluss/rand,dinfuehr/rust,robertg/rust,AerialX/rust,kwantam/rust,XMPPwocky/rust,mahkoh/rust,philyoon/rust,seanrivera/rust,omasanori/rust,erickt/rust,pythonesque/rust,servo/rust,KokaKiwi/rust,bombless/rust,sae-bom/rust,avdi/rust,cllns/rust,emk/rust,servo/rust,nham/rust,zubron/rust,barosl/rust,nwin/rust,jroesch/rust,GBGamer/rust,ebfull/rust,bombless/rust,ejjeong/rust,nham/rust,ejjeong/rust,mihneadb/rust,andars/rust,zachwick/rust,philyoon/rust,richo/rust,rprichard/rust,dwillmer/rust,bombless/rust,omasanori/rust,mihneadb/rust,zubron/rust,P1start/rust,dwillmer/rust,aidancully/rust,gifnksm/rust,omasanori/rust,pshc/rust,hauleth/rust,dinfuehr/rust,mdinger/rust,ebfull/rust,XMPPwocky/rust,AerialX/rust-rt-minimal,pshc/rust,jashank/rust,0x73/rust,defuz/rust,XMPPwocky/rust,victorvde/rust,erickt/rust,dwillmer/rust,P1start/rust,kimroen/rust,P1start/rust,pelmers/rust,P1start/rust,aneeshusa/rust,miniupnp/rust,ktossell/rust,mdinger/rust,stepancheg/rust-ide-rust,zubron/rust,mdinger/rust,aturon/rust,GBGamer/rust,ktossell/rust,mdinger/rust,arthurprs/rand,seanrivera/rust,nham/rust,zaeleus/rust,XMPPwocky/rust,l0kod/rust,zachwick/rust,AerialX/rust-rt-minimal,jroesch/rust,krzysz00/rust,defuz/rust,emk/rust,retep998/rand,zaeleus/rust,pythonesque/rust,emk/rust,Ryman/rust,ebfull/rand,reem/rust,jroesch/rust,cllns/rust,krzysz00/rust,ejjeong/rust,l0kod/rust,rprichard/rust,pczarn/rust,mahkoh/rust,stepancheg/rust-ide-rust,aidancully/rust,aidancully/rust,jashank/rust,AerialX/rust,jashank/rust,hauleth/rust,mvdnes/rust,mitsuhiko/rust,carols10cents/rust,jashank/rust,aepsil0n/rust,jbclements/rust,kwantam/rust,untitaker/rust,aidancully/rust,mitsuhiko/rust,ejjeong/rust,jbclements/rust,ktossell/rust,cllns/rust,zubron/rust,pshc/rust,aepsil0n/rust,krzysz00/rust,AerialX/rust-rt-minimal,servo/rust,zubron/rust,0x73/rust,miniupnp/rust,TheNeikos/rust,graydon/rust,pythonesque/rust,untitaker/rust,aturon/rust,erickt/rust,omasanori/rust,jashank/rust,kimroen/rust,hauleth/rust,untitaker/rust,omasanori/rust,jroesch/rust,defuz/rust,pczarn/rust,kwantam/rust,GBGamer/rust,l0kod/rust,seanrivera/rust,aturon/rust,robertg/rust,nwin/rust,untitaker/rust,kimroen/rust,aturon/rust,rohitjoshi/rust,jroesch/rust,Ryman/rust,jbclements/rust,AerialX/rust,mvdnes/rust,pythonesque/rust,pythonesque/rust,dinfuehr/rust,pczarn/rust,defuz/rust,quornian/rust,nham/rust,avdi/rust,gifnksm/rust,aturon/rust,bombless/rust,kwantam/rust,jbclements/rust,pczarn/rust,kwantam/rust,richo/rust,jbclements/rust,ruud-v-a/rust,sae-bom/rust,vhbit/rust,GrahamDennis/rand,hauleth/rust,kimroen/rust,nwin/rust,quornian/rust,nwin/rust,stepancheg/rust-ide-rust,mahkoh/rust,zubron/rust,erickt/rust,vhbit/rust,krzysz00/rust,mahkoh/rust,dinfuehr/rust,kwantam/rust,rohitjoshi/rust,mvdnes/rust,aneeshusa/rust,aepsil0n/rust,reem/rust,robertg/rust,mvdnes/rust,jroesch/rust,reem/rust,emk/rust,graydon/rust,michaelballantyne/rust-gpu,untitaker/rust,michaelballantyne/rust-gpu,mihneadb/rust,avdi/rust,pythonesque/rust,mihneadb/rust,victorvde/rust,victorvde/rust,0x73/rust,aepsil0n/rust,graydon/rust,barosl/rust,waynenilsen/rand,pshc/rust,philyoon/rust,quornian/rust,erickt/rust,jbclements/rust,nham/rust,pczarn/rust,pelmers/rust,jbclements/rust,achanda/rand,barosl/rust,XMPPwocky/rust,rprichard/rust,dinfuehr/rust,graydon/rust,AerialX/rust,GBGamer/rust,jbclements/rust,KokaKiwi/rust,andars/rust,nwin/rust,pczarn/rust,robertg/rust,mahkoh/rust,zachwick/rust,mitsuhiko/rust,nwin/rust,richo/rust,jroesch/rust,ruud-v-a/rust,l0kod/rust,kimroen/rust,gifnksm/rust,richo/rust,pshc/rust,miniupnp/rust,rohitjoshi/rust,carols10cents/rust,KokaKiwi/rust,rprichard/rust,0x73/rust,jbclements/rust,vhbit/rust,aidancully/rust,0x73/rust,carols10cents/rust,richo/rust,pelmers/rust,aepsil0n/rust,untitaker/rust,jashank/rust,stepancheg/rust-ide-rust,l0kod/rust,stepancheg/rust-ide-rust,gifnksm/rust,andars/rust,bombless/rust,robertg/rust,mihneadb/rust,TheNeikos/rust,ktossell/rust,reem/rust,miniupnp/rust,zachwick/rust,KokaKiwi/rust,kimroen/rust,quornian/rust,barosl/rust,omasanori/rust,krzysz00/rust,pelmers/rust,pshc/rust,mdinger/rust,michaelballantyne/rust-gpu,ruud-v-a/rust,jroesch/rust,pshc/rust,andars/rust,l0kod/rust,andars/rust,GBGamer/rust,miniupnp/rust,mvdnes/rust,avdi/rust,l0kod/rust,defuz/rust,AerialX/rust-rt-minimal,pczarn/rust,pelmers/rust,victorvde/rust,ebfull/rust,0x73/rust