is there some equivalent way to use safe navigation when using square bracket struct notation?

var env = server?.system?.environment ?: {};
if( env.keyExists(arguments.name) ) { ... }

to this: 

var env = server?.system?.environment?[arguments.name] ?: "";

or something similar. it's not hugely important to do the second way, just curious if there's a square bracket version of safe navigation

I cant give you a definitive answer but I have never got it to work

i'm sure there's a way to do it with evaluate() but i wouldn't bother if that's the case tbh.

adobe define it as an alternative to the dot . operator

You can use the safe navigation operator to access members of a Struct or values of an object.

Instead of ".", using the safe operator ensures that exception is not thrown when the variable is not defined.

right. just not sure it's worth

var myValue = evaluate("server?.system?.environment?.#arguments.name# ?: ''");

assuming that works

this is my version

return server.system.properties[ settingName ] ?: server.system.environment[ settingName ] ?: defaultValue;

Won't that crash if system doesn't exist in server, etc?

yes it would but someone would have to delete it from the scope and I would be very cross if they did

understood, but we have no idea about @websolete's use case, he was asking about the syntax for safely navigating through a possibly incomplete hierarchy.

to be clear, my use case is a application.cfc method to return environment vars, the method as it stands now (lucee 5.x):

/**
	 * Returns the specified environment variable
	 *
	 * @name string 					the name of the env variable in the server.system.environment scope
	 * 
	 * @throws InvalidEnvVariable 		thrown when the specified variable does not exist
	 * 
	 * @return any 
	 */
	private any function getEnvVar( required string name ) {
		var env = server?.system?.environment ?: {};
		if( len(arguments.name) && env.keyExists(arguments.name) ) {
			return env[arguments.name];
		}
		else {
			throw( type="InvalidEnvVariable", message="The specified environment variable [#arguments.name#] does not exist" );
		}
	}

I just... erm... tried it... https://trycf.com/gist/a431e29bb1cedbbcd82981276184aaf3/acf2021?theme=monokai

st = {
    "DOES_EXIST" = "some value"
}

writeoutput(st?["DOES_NOT_EXIST"]) // undefined
writeoutput(st?["DOES_EXIST"]) // some value

key = "DOES_NOT_EXIST"
//writeoutput(st?[key]) // Error: Invalid CFML construct

Note that it only seems to work with string literals. Not with variables. Someone who cares should perhaps raise a bug for that (ping @Mark Takata (Adobe)) Doesn't work at all on Lucee. See above re "someone who cares ~"