let(::loveThePet)

invokes

let

on the receiver object using

loveThePet

as the function parameter

they are very different expressions

let{::loveThePet}

would be equivalent to

let({ ::loveThePet })

or

val func = { ::loveThePet }
item.let(func)

What you’d be doing, in essence, is passing to

.let()

a lambda that discards its arguments and simply returns that method reference, which is why you get a signature error and end up with a transform that leaves you with a

KFunction

the requisite expression would therefore look more like this

returnHuman("name")
    .let(::saveAHumanReturningABall)
    .let(::kickTheBallReturningABall)
    .let(::keepTheBallReturnAPet)
    .let(::loveThePet)

assuming those functions are member declarations and not just local variables

if they are just local variables, the

::

is not needed to qualify based on namespace