client.connect tested for true?

Hello,

One can see in many example the statement

if(client.connect)

yet in the reference it is stated that client.connect possible return values are {-4, -3, -2, -1, 1} don't these all evaluate to true?'

aamof, I have a code which, under certain conditions, consistently seems to succeeds in
if (client.connect)
and exits the following
while (client.connected())

'seems' because its a deduction from log data

Thanks

implementations only return 0 or 1. I checked esp8266, Ethernet, UIPEthernet, WiFiEsp