Return same object as argument

Question

This is probably an anti-pattern, but I want to return the same object as an argument, in this case like so:

const handleConnection = (s: net.Socket): net.Socket => {

  s.pipe(createParser()).on('data', (d: any) => {

    log.info(chalk.green.underline('dygrep server response:'));

    if (d && d.lastMessage) {
      process.stdout.write(prompt);
    }

  });

  return s;

};

so what would be ideal is to do something like this:

const handleConnection = (s: net.Socket): s => {

  s.pipe(createParser()).on('data', (d: any) => {

    log.info(chalk.green.underline('dygrep server response:'));

    if (d && d.lastMessage) {
      process.stdout.write(prompt);
    }

  });


  return s;

};

but yeah that's not quite right - how do I tell TypeScript that I am returning one of the arguments?

Are you trying to enforce in compile-time the fact that the argument and return value are not only of the same type, but necessarily the same object? — Cerberus, Sep 18 '18 at 04:14

score 1 · Accepted Answer · answered Sep 18 '18 at 04:03

1

how do I tell TypeScript that I am returning one of the arguments

Generics. The constraint is the return is same as argument e.g.

function handleConnection<T extends net.Socket>(arg:T):T{}

Here whatever is passed in as arg is what is returned.

answered Sep 18 '18 at 04:03

basarat

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you sure I couldn't return a new net.Socket instance tho? To me, that seems possible given the typings. – Alexander Mills Sep 18 '18 at 04:52

Return same object as argument

1 Answers1