Support default values about emboss HOT 4 OPEN

Should Ok() also fail if the value of the field is not the default/fixed value? In the case of commands with op codes, the view should be invalid if it is not the specified value.

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Ok() falls under the (existing) feature, [requires].

However, ideally, [default_value] (or whatever it gets called) would be inferred from annotations like [requires: this == 10], without a human having to explicitly add it.

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Just to make sure, I think we can infer the default value from the requires annotation if it's there and only a scalar value. AFAIK, the requires annotation allows for ranges as well and we can't infer much there. We also need to be able to set a default value which can be overridden to something else if necessary. Just want to make sure the implementation captures all these use cases.

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That is correct. The exact rules I am thinking are:

1. If the field is a structure (struct or bits type), its default value is the compound of the default values of its fields.
2. Otherwise, if there is a [default_value: n] annotation on the field, the default value is n.
3. Otherwise, if there is a [requires] annotation of the form [requires: this == n] or [requires: n == this], where n is a compile-time constant (including an expression that evaluates to a compile-time constant, like 2 * Type.some_constant), then the default value is n.
4. Otherwise, if the field is a boolean and there is a [requires] annotation of the form [requires: this], the default value is true.
5. Otherwise, use the default default value for the field's type, which should be 0 for numeric types and false for booleans.

I am open to other inference forms, but I cannot think of any that would be useful and seem likely in real code.

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