Allow one-time binding for ng-model when ng-model-options getterSetter is true

[FstTesla]

Do you want to request a feature or report a bug?

Feature.

What is the current behavior?

The expression in ng-model directive is evaluated always, even if it is prefixed with ::, which is the correct and reasonable behavior. Anyway, when ng-model-options is present and getterSetter is true, one-time binding could be profitably honored, especially if the model expression evaluates to a getter-setter factory function.

Minimal demo of the problem

Demo. By opening the console, one can see that the ng-model expression is not evaluated once.

What is the expected behavior?

When ng-model-options is present (directly or by inheritance from parent elements) and getterSetter is true, honor one-time binding if specified in the ng-model expression.

What is the motivation / use case for changing the behavior?

In the given conditions, the expression returns a function that may or may not change. If it does not change, the overhead of evaluating it every time can be removed. Moreover, if such getter-setter function has some context to be preserved from call to call, one-time binding would remove the need to manually cache it.

[gkalpak]

I am not sure how much work it requires (because the current implementation expects the ng-model expression to be a direct reference to a function). It is probably not worth it imo (considering it won't be a trivial change).

As a work-around, you can achieve a similar behavior by using ngInit to initialize the getterSetterFn:

<input
    ...
    ng-init="getterSetterFn = getterSetterFactory(surname)"
    ng-model="getterSetterFn"
    ng-model-options="{getterSetter: true}" />

Demo

[Thaina]

@gkalpak If we have many consecutive init with the same name like that would it not conflict?

<input ng-init="getterSetterFn = getterSetterFactory('name')" ng-model="getterSetterFn" ng-model-options="{getterSetter: true}" />

<input ng-init="getterSetterFn = getterSetterFactory('surname')" ng-model="getterSetterFn" ng-model-options="{getterSetter: true}" />

??

edit: It seem like it conflict and cannot be used. Alternatively we should have some directive to make a scope variable instead of ng-init

[gkalpak]

@Thaina, of course it will conflict if you use the same variable name on the same scope. It is trivial to create your own version of ngInit that also creates a new scope, but the simplest thing to do here is use a unique variable name:

<input
    ng-init="nameGetterSetterFn = getterSetterFactory('name')"
    ng-model="nameGetterSetterFn"
    ng-model-options="{getterSetter: true}" />

<input
    ng-init="surnameGetterSetterFn = getterSetterFactory('surname')"
    ng-model="surnameGetterSetterFn"
    ng-model-options="{getterSetter: true}" />

BTW, this is not related to this issue, because the name conflict would be present regardless if one-time binding is supported for getterSetter in ngModel or not.