What gulp.src() → gulp.dest() returns and why it works in gulp#4.x?

Question

According gulp#4.x documentation, gulp task must return the one of the following:

• stream
• promise
• callback function
• child process
• RxJS Observable

However, the following task working without error:

gulp.task('test', () => {
    return gulp.src('source/**/*.*')
            .pipe(gulp.dest('dest'));
});

But what of the above ones it returns?

Answer 1

From the docs, gulp.src:

Returns a stream of Vinyl files that can be piped to plugins.

And gulp.dest:

...will write files [and]... Re-emits all data passed to it so you can pipe to multiple folders