Higher order function, stream type annotations

Question

I am trying to write some simple, functional examples for evaluating a flow type system. I am missing something obvious or this pattern should work:

function logger (message: string): void {
    console.log(message);
}

function consumer (logFunc: logger) {
    logFunc('foo');
}

consumer(logger);

When I try it on tryflow.org , I get "Signed signature not found in prototype." I get the same message on local start (thread 0.21.0):

  8:     logFunc('foo');
         ^^^^^^^^^^^^^^ function call. Callable signature not found in
  8:     logFunc('foo');
         ^^^^^^^ prototype

I can solve the problem by explicitly declaring the type alias, but this seems like unnecessary duplication (especially for more complex modules):

type loggerType = (message: string) => void;

function logger (message: string): void {
    console.log(message);
}

function consumer (logFunc: loggerType) {
    logFunc('foo');
}

consumer(logger);

The only relevant documentation I have found so far: http://flowtype.org/docs/functions.html#function-based-type-annotations

, consumer logger (, npm) , logger (es6 commonJS).

• (logger loggerType).
• logger consumer - , logFunc logger. , .

, ?

Answer 1

typeof:

function consumer (logFunc: typeof logger) {
    logFunc('foo');
}

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