in swift code please Example code: extension Car $\{$

mutating func emptyGas$($amount: Double$)\{$

precondition$($amount && amount $>0,$

"Amount to remove must be between $0$ and $1.")$

gasLevel $-=$ amount

$\}$

mutating func fillGas$()\{$

gasLevel $=1\mathrm{.}0$

$\}$

$\}$