Binding an array in polymer and detecting changes in a child component - arrays

Question

I have a component in Polymer that has an array as one of its properties.
Then I have a child component to which I'm passing this array. What I'm trying to do is to detect a change in that array from the child component.
Here is the parent component:
<dom-module id="some-test">
<template>
<paper-input label="Let's update param" on-input="updateParam"></paper-input>
<some-child param={{param}}></some-child>
</template>
<script>
Polymer({
is: 'some-test',
properties: {
param: {type: Array, value: []}
},
updateParam: function(e) {
this.param["test"] = e.currentTarget.value;
console.log("Param has been updated");
}
});
</script>
</dom-module>
And here is the child component:
<dom-module id="some-child">
<template>
<div>the child component</div>
</template>
<script>
Polymer({
is: 'some-child',
properties: {
param: {type: Array, observer: "doSomething"},
},
doSomething: function() {
console.log("ah, we've detected a change in param");
},
});
</script>
</dom-module>
So, when I type something in the input field (in the first component), I get a consolge log of "Param has been updated". All good.
But then I would except param to be passed to the child component, which would detect the change and log "ah, we've detected a change in param".
However this doesn't seem to happen. If I use a string instead of an array, then it works as intended. But if it's an array and I update one of its values, the child component doesn't pick up the change.
This leads me to believe I am missing something as to how to bind an array. Any clues?

Answer 1

You can use complex observers in child components:
<dom-module id="some-child">
<template>
<div>the child component</div>
</template>
<script>
Polymer({
is: 'some-child',
properties: {
param: {type: Array, observer: "doSomething"},
},
//Here add complex observers
observers: ['doSomething(param.*)', 'doSomething(param.splices)'],
doSomething: function() {
console.log("ah, we've detected a change in param");
},
});
</script>
</dom-module>

Answer 2

Ah, I finally got it working! It took a combination of the various answers. Here is the final code that works:
Parent component:
<dom-module id="some-test">
<template>
<paper-input label="Let's update param" on-input="updateParam"></paper-input>
<some-child param={{param}}></some-child>
</template>
<script>
Polymer({
is: 'some-test',
properties: {
param: {type: Array, value: []}
},
updateParam: function(e) {
this.set("param.test", e.currentTarget.value); <!-- this is the first trick -->
console.log("Param has been updated");
}
});
</script>
</dom-module>
And here is the child component:
<dom-module id="some-child">
<template>
<div>the child component</div>
</template>
<script>
Polymer({
is: 'some-child',
properties: {
param: {type: Array},
},
observers: [
"doSomething(param.*)"
]
doSomething: function() {
console.log("ah, we've detected a change in param");
},
});
</script>
</dom-module>
So, the two things that I needed to do were:
1) Use "this.set()" to update the value of the object in the parent component
2) Use a complex observer in the child component