Checking for readonly in Geb - groovy

Question

I'm trying to write a test in Geb that has a bunch of different text fields. The scenario is essentially that there are five or six html inputs and the user should only be allowed to type in one of them at a time. That is, if the first textbox has a value, the rest of the boxes should be immutable.
Instead of the element having an input type="disabled", they have an attribute (I'm assuming it's an attribute?) of readonly.
Here is a generic example:
<input aria-labelledby="Date Input Value 1" id="Date Input 1" name="Date Input 1" class="input-small DateOrEmpty dateInput" value="" style="display: inline-block;" readonly="">
I've tried
${"input", id: "Date Input 1"}.#readonly
as well as
${"input", id: "Date Input 1"}.has("readonly")
and I haven't had much luck..

Answer 1

Instead of having to deal with the fact that even an empty readonly attribute will cause the element to be read only but $("input[id='Date Input 1']").#readonly evaluates to a falsey value (as #readonly returns the value of the attribute which is an empty string in your case) why not turn the navigator into an instance of FormElement module and use the isReadOnly() property method it provides?
$("input[id='Date Input 1']").module(FormElement).readOnly
EDIT
As pointed out by kriegaex, $("input[id='Date Input 1']").#readonly actually evaluates to a truthy value (because WebDriver always returns a string which contains true when obtaining the value of readonly attribute as long as the attribute is defined on the element and regardless of the actual value of that attribute).
The above means that:
$("input[id='Date Input 1']").module(FormElement).readOnly
and:
$("input[id='Date Input 1']").#readonly
are equivalent in that they evaluate to a truthy value.

Answer 2

You have several problems here:
You use HTML IDs with inline spaces. This are actually not legal names and make it more difficult to write simple CSS selectors like #my-id for them.
Geb syntax for selectors uses parentheses, not curly braces. Curly braces are used for closures, which are a completely different kind of beast.
Please note that according to HTML specification the readonly attribute is boolean and always true if it exists at all, i.e. usually you do not write readonly="something" but just readonly. Even if you write readonly="false" it will evaluate to true because its value is ignored, only its existence is checked.
So if you have this HTML code:
<input id="Date Input 1" readonly>
<input id="Date Input 2">
<input id="date-input-3" readonly="false">
<input id="date-input-4">
<input id="date-input-5" readonly="">
You can write these selectors in your Geb test (please note how not using spaces in IDs makes the selectors simpler):
$("input[id='Date Input 1']").#readonly
!$("input[id='Date Input 2']").#readonly
$("input#date-input-3").#readonly
!$("input#date-input-4").#readonly
$("input#date-input-5").#readonly