Why does fluorine stabilise a carbocation? [duplicate]

I have read that halogens have a stonger -I (inductive effect) than +M (mesomeric effect),then why do they stabilise a carbocation instead of destabilising it?

I asked this doubt to my teacher and he said that halogens like fluorine do not exert -I on a carbocation and hence they stabilise a carbocation through +M,is this true?

Fluorine belongs to the same period as Carbon. Carboncation is electron deficient which has its two $2p$ orbitals vacant. One electron of carbon in $2p$ goes into the formation of $\ce{C-F}$ $\sigma$ bond. $\ce{F}$ has $2p$ orbital containing a lone pair which can be donated to the $2p$ vacant orbitals of carbocation. Same size $2p$ orbitals of Carbon and Fluorine overlap effectively to form a $\pi$ bond.